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Guide
Dual-Date Coins UK: Mules, Errors and What They're Worth
A dual-date coin is one where the obverse and reverse don't match in date logic, an
old design paired with a new, or two design generations crossed at the press. The two famous UK
examples are the 1983 NEW PENCE 2p (a 1983-dated coin still reading the 1971-81
legend) and the 2008 undated 20p mule (no date anywhere on the coin). Together
they're the headline UK mules. This guide covers how dual-dates happen at the Royal Mint,
how to identify a real one versus a damaged or counterfeit lookalike, realised auction prices
and how to sell what you've found.
The 1983 NEW PENCE 2p mule. A 1983-dated obverse paired in error with the obsolete NEW PENCE reverse die used 1971–1981, instead of the new TWO PENCE die introduced for 1983 onwards. Believed to be confined to 1983 Royal Mint proof sets. Realised auction prices: £500–£2,500 depending on grade and slab status.
In brief. A "dual-date" or "mule" is a UK coin struck from
two dies that should never have been paired. The two famous cases: 1983 NEW PENCE 2p
(1983 obverse + obsolete NEW PENCE reverse, found in 1983 proof sets, £500–£2,500)
and 2008 undated 20p (pre-2008 obverse + post-2008 reverse, no date anywhere,
£50–£200, ~50,000–250,000 in circulation). Both are the result of design
transitions where new and old dies coexisted briefly. Counterfeits and date-altered fakes are
common; authenticate any candidate worth over £100 before paying. Sell via specialist
auction (Spink, Baldwin's, Noonans) for top realisations or eBay with grading slab for
speed.
Watch£2000! DUAL DATED £1 COIN 2016 ERRORThe dual-dated 2016 £1 error (Dans Dollars) Video: Dans Dollars on YouTube
What is a dual-date coin?
Modern coin striking uses two dies fitted on a press: an obverse die (the
portrait side) and a reverse die (the design side). When the Royal Mint changes
the design of either side, new dies are produced and the old dies retired. The transition
period is when mules happen.
A mule occurs when a die from the old design generation is mistakenly fitted alongside a die
from the new generation. The resulting coin shows two faces that were never meant to coexist on
the same piece. Three flavours:
Cross-generation mule. Old obverse die paired with new reverse, or vice
versa. Both UK headliners are this type: 1983 NEW PENCE (old reverse + new obverse) and
2008 undated 20p (old obverse + new reverse). Visible because the date logic of the two
sides doesn't match.
Cross-denomination mule. A die meant for one denomination paired with the
die for another. Rare in modern UK production but documented in earlier eras.
Twin obverse / twin reverse. Two obverse dies or two reverse dies fitted
together by mistake. Extreme rarity. Almost no documented modern UK examples.
The defining feature of a dual-date coin is that the strike itself is normal:
sharp, clean, all design elements correctly raised. The error is in the pairing, not the
striking. This is what distinguishes a mule from physical post-mint damage.
Following decimalisation in 1971, the new decimal pence carried the legend NEW PENCE
on the reverse to distinguish them from the soon-to-be-demonetised pre-decimal pennies. The
transitional NEW PENCE legend was used 1971–1981. From 1982 onwards (1p) and 1983 onwards
(2p), the Royal Mint changed the legend to ONE PENNY and TWO PENCE
respectively, signalling the end of the transition.
The 1983 2p was the first year for the TWO PENCE legend. New reverse dies were produced. The
old NEW PENCE reverse dies were due to be retired. But during the striking of 1983
Royal Mint proof sets, an old NEW PENCE reverse die was mistakenly fitted on the
proof press for a small batch. The result: 1983-dated proof 2p coins reading NEW PENCE instead
of TWO PENCE.
Three things to know about this error:
It's confined to proof sets. Authentic 1983 NEW PENCE 2ps are
encapsulated proofs, not loose circulation coins. Earlier-dated coins (1971–1981) all
read NEW PENCE and are common at face value, those are not the error. The error is
specifically a 1983 specimen reading NEW PENCE.
Mintage is unknown but small. The Royal Mint hasn't published a
figure. Best estimates put the 1983 NEW PENCE proof error at a few thousand
sets across the year's proof issue.
Realised prices. £500–£1,500 for raw specimens;
£1,000–£2,500 for slabbed PR-65+ examples. The error is one of the
most-fakèd in UK numismatics; authentication is essential.
The 2008 undated 20p mule
The most famous UK error and the most findable in change. Detailed coverage in our dedicated
guide; here is the mechanism summary:
Until 2008, the 20p carried the date on the reverse (Tudor Rose design). The
2008 redesign, Matthew Dent's "Royal Shield" series, where the 1p, 2p, 5p,
10p, 20p and 50p reverses each show a piece of the Royal Coat of Arms shield, moved the
date to the obverse. So pre-2008 20ps had date on reverse and post-2008 20ps had date on
obverse.
During the die-set transition in 2008, a small batch of 20ps was struck pairing the new (now
dateless) reverse with an old (still dateless) obverse from the previous design generation. The
result: a 20p with no date anywhere on the coin. They were released into
circulation undetected and only spotted later.
Estimates of how many entered circulation: 50,000 to 250,000, though the Royal
Mint has not published a definitive figure. The undated 20p remains legal tender. Realised
prices: £50–£100 for circulated specimens, £100–£200
for UNC. For full coverage including how to spot a real one versus a date-filed counterfeit,
see our 2008 Undated 20p Mule guide.
Why mules happen at the Royal Mint
The Royal Mint produces around 2 billion coins a year. Mules are vanishingly
rare in percentage terms but inevitable at that volume. The operational pathways for mules to
enter circulation are well-documented:
Die transition periods. When a design changes, new and old dies briefly
coexist in tooling stores. The wrong die can be selected for fitting if the labels are
ambiguous or the press operator is rushed. Almost all UK mules trace to design transitions:
1983 (new TWO PENCE legend), 2008 (new Royal Shield series), 2017 (new 12-sided £1).
Multi-press production. The Royal Mint runs many presses simultaneously,
each on a specific denomination. Cross-press contamination, a die from one press
ending up on another, happens occasionally during shift changes or maintenance.
Quality control gaps. Standard QC samples a small fraction of struck
coins. Visible errors caught at QC are recycled. But errors not caught at QC, particularly
subtle ones, can pass through to bagging and dispatch.
Proof set production. Proof sets use slower presses with more careful
inspection, but errors still slip through, particularly when the proof striking
coincides with a design change. The 1983 NEW PENCE error is a classic example.
Modern automated systems have substantially reduced the mule error rate, but not eliminated
it. The Royal Mint has confirmed several minor mule incidents since 2010 in addition to the
famous 2008 undated 20p.
How to identify a real dual-date error vs a damaged coin
The single most important distinction in error coin authentication: strike vs
damage. A genuine mint error has a normal, sharp strike with all design elements
correctly raised, just different from the intended pairing. Post-mint damage
disrupts the surface or alters the design after the coin has left the mint.
Five tests to distinguish:
Surface integrity. A real error has clean, even mint surfaces. Damage
shows scratches, gouges, abrasion patterns, file marks or chemical staining.
Design relief. All design elements should sit at normal, full relief.
If the "missing" element area is recessed below field level, it's been
ground or filed off, not a mint error.
Edge. Mint errors have normal edges. Filed-off-date counterfeits often
show edge damage from clamping during the alteration.
Weight and dimensions. A real error matches the host coin's spec
exactly. Wrong weight or diameter usually means counterfeit, not error.
Die-pair consistency. The two faces should each look like a normal Royal
Mint strike for their respective design generation. If the "old" face looks
unusually crude or the legend spacing is wrong, the coin may be a fantasy piece struck
outside the mint.
If the coin passes all five tests. Don't clean it. Don't handle
the surfaces. Place it in an inert flip or 2x2 holder, photograph both sides under raking
light, and submit it to a grading service: CGS UK, NGC or PCGS. Fees of £20–£50
per coin are negligible against a £500–£2,500 realisation, and the slab adds
significant resale value. For coins worth £100–£500, slabbing is still
worthwhile because eBay and dealer buyers pay 30–50% more for verified errors.
Realised auction prices for known dual-date errors
Error
Year
Coin
Typical realised range
NEW PENCE on 1983 proof
1983
2p (proof)
£500–£2,500
Undated mule
2008
20p
£50–£200
Wrong-planchet decimal strike
1971–1972
2p on halfpenny blank
£500–£1,500
Die-rotation 180° error
2014–2017
£2 (Magna Carta, Shakespeare etc)
£30–£100
Missing edge inscription
Various
£2 bimetallic (esp. Newton)
£25–£75
Brockage (struck-coin sticking to die)
Various
Various
£500–£3,000
Off-centre strike (15%+)
Various
50p, 20p
£15–£100
Pattern / specimen mules (non-public)
Various
Various
£1,000–£10,000+
Ranges drawn from realised auction figures at Baldwin's,
Spink,
Noonans and dealer
listings. Top of each band assumes slabbed authenticated examples in upper-grade preservation.
Selling a dual-date error you've found
The right venue depends on the coin's value tier. Three options, ranked by typical
realised return:
Specialist auction. For slabbed authenticated coins worth £500+,
consign to Spink,
Baldwin's or
Noonans. Hammer
commissions 15–20% but realisations on rare errors typically beat any private offer.
Timeline: 3–6 months from consignment to settlement.
eBay UK with grading slab. For coins worth £100–£500, a
slabbed listing with clear photos and authentication certificate sells reliably and
quickly. Listing fees are minimal and final-value fees ~12.8% plus payment processing.
Avoid raw listings for valuable errors, buyers refuse to pay top prices for
unverified coins.
Specialist dealer cash purchase. Coin dealers focused on errors will buy
privately for cash. Typical offer: 60–75% of likely auction realisation in exchange
for the speed and certainty. Useful for the 2008 undated 20p where auction commission
eats into a modest selling price.
Avoid generic estate dealers, jewellers and high-street antique shops, none recognise or
pay for numismatic premium on errors. Avoid Facebook Marketplace and similar peer-to-peer
platforms unless you can meet the buyer in person and the coin is slabbed.
Risk: fake mules in the secondary market
Both the 1983 NEW PENCE 2p and the 2008 undated 20p are heavily faked because they're
famous, easy to describe and command four-figure prices in top grade. Three common counterfeit
techniques:
Filed-off date 20ps. A normal 2008-onwards 20p has the date area on the
obverse ground, filed or chemically etched until the digits are no longer visible. Tell-tale:
the field around where the date should be is slightly recessed below the surrounding metal,
or shows fine abrasion patterns under raking light. A genuine undated mule has a clean,
original obverse with no signs of work.
Mislabelled NEW PENCE 2ps. Sellers offer a normal 1971–1981 NEW PENCE
2p (which read NEW PENCE legitimately) as the "1983 error". Tell-tale: the date
is wrong. The genuine error is specifically 1983-dated. Always check the obverse date
before paying.
Counterfeit struck pieces. Outright fakes struck outside the Royal Mint,
sometimes very convincing visually but failing on weight, alloy or edge profile. Tell-tale:
weight off the host coin's spec by more than ±0.05 g; alloy colour slightly
wrong (golden brass instead of copper-plated steel for the 2p, etc.); edge seams or
unusually crude reeding.
For any candidate worth more than £100, professional grading from CGS UK, NGC or PCGS is
the only way to settle the question definitively. The slab and certification are also what eBay
buyers and auction houses require for top-end pricing.
In strict numismatic usage, a dual-date coin (or "mule") is one struck from two dies that were never meant to be paired, typically the obverse from one design generation paired with the reverse from another. The result is a coin where the two faces are mismatched in date logic: an old design generation paired with a new, or two different reverses, or two different obverses. The classic UK dual-date is the 2008 undated 20p, where a pre-2008 obverse (no date) was paired with a post-2008 reverse (no date), producing a 20p with no year on either side. The 1983 New Pence 2p is also a mule: a 1983-dated obverse paired with the obsolete 1971–1981 NEW PENCE reverse rather than the new TWO PENCE reverse.
How does the 1983 "New Pence" 2p error work?
In 1983 the Royal Mint changed the legend on the 2p reverse from NEW PENCE (the transitional decimalisation legend used 1971–1981) to TWO PENCE. The intended design was the new TWO PENCE wording for all 1983-dated coins. But during the proof-set striking that year, an old NEW PENCE reverse die was accidentally fitted on the press for a small batch. The result: 1983-dated proof 2p coins reading NEW PENCE instead of TWO PENCE. The error is believed to have been confined to 1983 Royal Mint proof sets rather than circulation, so most authentic specimens are encapsulated proofs. Realised values: £500–£1,500 for raw specimens, £1,000–£2,500 for slabbed PR-65+.
How does the 2008 undated 20p mule work?
The 2008 redesign of the 20p (Matthew Dent's "Royal Shield" series) moved the date from the reverse to the obverse. Pre-2008 20p coins had the date on the reverse (the Tudor Rose design). Post-2008 20p coins had the date on the obverse (the new portrait + date layout). During the die-set transition, a small batch was struck pairing the new (now dateless) reverse with an old (still dateless) obverse, producing a 20p with no date anywhere on the coin. Estimates of how many entered circulation range from 50,000 to 250,000. The Royal Mint has not published a definitive figure. Current value: £50–£100 for circulated, £100–£200 for UNC.
Why do mules happen at the Royal Mint?
Modern coin striking uses two dies (one obverse, one reverse) mounted on a press. Mules occur when a die from one design generation is mistakenly fitted on the press alongside a die from another generation, or when a die meant for one denomination is fitted alongside the wrong reverse. Three operational scenarios drive most UK mules: (1) design transitions, where new and old dies coexist briefly in the press tooling stores (1983 NEW PENCE, 2008 20p); (2) denomination crossover, where a die meant for, say, a 2p is fitted alongside a 1p reverse; and (3) inspection failures, where the QC step that should have caught the wrong die didn't. Modern automated systems have reduced but not eliminated the risk. The Royal Mint produces ~2 billion coins a year; even a 0.001% error rate yields tens of thousands of error coins.
How do I tell a real dual-date error from a damaged coin?
Two key checks. First, the strike must be normal: a genuine error has a clean, sharp strike with all design elements correctly raised, just different from the intended pairing. If the date is "missing" because the digit area is scratched, filed, ground or chemically etched, that's post-mint damage, not a mint error. Second, compare to a documented reference: the 2008 undated 20p has been heavily photographed and any genuine specimen should match precisely in legend spacing, design relief and edge profile. Counterfeits where the date has been filed off a normal 2008-onwards 20p typically show file marks where the date used to be on the obverse, or distinct grinding patterns. For any candidate worth more than £100, professional grading from CGS UK, NGC or PCGS settles the question definitively.
How can I sell a dual-date error coin?
Three venues, ranked by typical realised value. (1) Specialist auction. For coins authenticated and slabbed: Spink, Baldwin's or Noonans auctions. Hammer commissions 15–20%; works best for £500+ pieces. (2) eBay UK with grading. A slabbed authenticated error sells for 30–50% more than a raw equivalent. List with clear photos showing the specific error feature (the missing date, the wrong legend, etc.) and full grade certification. (3) Specialist dealers. Coin dealers that focus on errors will buy private treaty for cash but typically pay 60–75% of likely auction realisation in exchange for the speed. For a £50–£100 circulated 2008 mule, dealer cash is often the simplest path; for a £1,500 1983 NEW PENCE proof, auction is worth the wait.
Are fake dual-date coins common?
Yes, increasingly so. The 2008 undated 20p and the 1983 NEW PENCE 2p are both heavily faked because they're famous, easy to describe and command four-figure prices in top grade. Three common counterfeit techniques: (1) Filed-off date 20ps, where the date area on a normal 2008-onwards coin has been ground or filed flat. Tell-tale: the field around where the date should be is slightly recessed or shows abrasion patterns; (2) Cleaned and polished "1983 New Pence" 2ps that aren't actually error coins but heavily-handled normal 1971–1981 NEW PENCE coins relabelled as "1983 error". Tell-tale: the date is wrong; (3) Counterfeit struck pieces from outside the Royal Mint, sometimes very convincing visually but failing on weight, alloy or edge. Authentication is essential for any error worth over £100.
Are there any other UK dual-date / mule errors I should know about?
A handful of confirmed mules sit alongside the 1983 and 2008 headliners. 1971–1972 New Pence wrong-planchet strikes, pieces struck with the new decimal design on a planchet meant for a different denomination, mostly 2p reverses on halfpenny blanks. Realised: £500+. 2014–2017 £2 die-rotation errors, the obverse and reverse misaligned by 180°, producing an upside-down reverse when flipped top-to-bottom. Realised: £30–£100. Missing edge inscription £2 coins, particularly the Newton-edge varieties, the bimetallic strike skipped the edge-inscription step. Realised: £25–£75. None match the 1983 or 2008 in fame or realised value, but all are legitimate Royal Mint errors with documented populations.
How can I check if my coin is a dual-date error?
Five-step home check: (1) Identify the year and denomination, use our catalogue to look up the design that should be on a normal coin of that year; (2) Compare the actual coin to the documented reference photos; (3) Look for the specific error feature, missing date, wrong legend, or design generation mismatch; (4) Verify weight and dimensions, a genuine error matches the host coin's spec exactly. Wrong weight or diameter means it's a counterfeit, not an error; (5) Check the edge and surface, a real error has clean, normal mint surfaces. If the date area shows file marks, abrasion or chemical staining, it's post-mint damage, not a mint error. If the coin passes all five checks, send it to a grading service; if it fails any one, it's likely not the error you think.
Why are dual-date errors more valuable than other errors?
Three reasons. First, they're visually striking: a coin with no date or the wrong legend is immediately, obviously different. That visibility drives both collector demand and media coverage, which feeds back into price. Second, they're narrow in population: a mule is the result of a specific die-pair mistake during a single production run, typically yielding hundreds to a few hundred thousand pieces, versus minor errors (off-centre strikes, die cracks) that can occur sporadically across millions of coins. Third, they're documented: the 2008 mule and 1983 NEW PENCE are both written up in Royal Mint and numismatic literature, which gives buyers confidence in the authenticity story. Together, these factors push dual-date errors into the upper tier of UK error coin pricing.
Should I get a dual-date error professionally graded?
Yes, for anything worth more than about £75. A slabbed authenticated error sells for 30–50% more than a raw equivalent, mostly because eBay and dealer buyers refuse to pay top prices for unverified errors after several years of fake-error scams. For UK coins, three grading services are widely recognised: CGS UK (British, lower fees, faster turnaround); NGC (American, second-largest globally, strong on UK errors); and PCGS (American, premium pricing). Fees typically £20–£50 per coin. Turnaround 4–12 weeks. The Pop Reports each service publishes also help you understand how scarce your specific error grade actually is.
Are dual-date errors still legal tender?
Yes. A mule or undated coin is still issued currency and remains legal tender at face value, you could spend the 2008 undated 20p as 20p, the 1983 NEW PENCE 2p as 2p. The Royal Mint does not run a recall or buyback programme for circulating errors; they treat them as legitimate issued currency. The numismatic premium, the £50, £500 or £1,500 above face value, is purely a secondary-market phenomenon driven by collector demand. From a tax perspective, gains on UK legal tender coins are exempt from Capital Gains Tax under HMRC manual CG78308, including error coins, which is a meaningful advantage at the higher value tiers.
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