UK Coin Errors List: Every Famous British Mint Mistake and What It's Worth

The Royal Mint produces around 2 billion coins a year. With volumes that high, mistakes happen occasionally and a small percentage end up in circulation before they're caught. The most famous British errors are listed below with realised secondary-market prices, identification notes, and how to tell a real error from post-mint damage. The 1983 "New Pence" 2p and the 2008 undated 20p are the headliners; everything else here is also genuinely tradeable.

Last updated: 6 June 2026

In brief. A "coin error" or "mint error" is a coin that left the Royal Mint with something wrong: missing date, wrong-pairing dies (a "mule"), off-centre strike, inverted effigy, wrong-blank, or missing edge inscription. The most valuable widely-known UK error is the 1983 "New Pence" 2p at £500–£1,500. The most famous and most findable in change is the 2008 undated 20p mule at £50–£100. Errors retain most of their premium even at low grades because rarity is in the strike, not the condition.

What counts as a coin error

A genuine mint error is a deviation from the intended design or strike that happened during production at the Royal Mint, before the coin entered circulation. The five main types, in rough order of frequency:

Die mismatch (mule): two dies paired that were never meant to be. Almost always rare.
Off-centre strike: die not centred over the planchet during striking, leaving the design partially off the coin.
Wrong planchet: a coin struck on a blank meant for a different denomination (a 2p struck on a 1p planchet, etc).
Die rotation / inverted effigy: the obverse and reverse dies are mounted at the wrong rotation, so flipping the coin top-to-bottom shows the reverse upside-down.
Die cap / brockage: a coin gets stuck to the upper die and strikes the next planchet, producing a coin with the design twice (or mirrored).

What is not a coin error: post-mint damage, deliberate alteration ("hobo" coins, ground-down edges, drilled holes), corrosion / chemical staining, normal die wear, or any "feature" that turns out to be a deliberate design variant. If a coin shows clear signs of impact, abrasion or chemical interference, it's damaged, not erroneous.

The famous British coin errors with realised values

1983 "New Pence" 2p

The headline UK error. In 1983 the Royal Mint changed the legend on the 2p from "NEW PENCE" (used 1971–81 during the decimalisation transition) to "TWO PENCE". When proof sets were struck for 1983, a small batch accidentally used the old "New Pence" reverse die, producing 1983-dated 2p coins with the obsolete legend. The error coins are believed to have been issued only in 1983 Royal Mint proof sets (not loose coinage), so authentic specimens are encapsulated proofs.

Realised prices: £500–£1,500 for raw specimens; £1,000–£2,500 for slabbed PR-65+.
How to identify: 1983 date, 2p coin, reverse legend reads "NEW PENCE" instead of "TWO PENCE".
Beware: earlier-dated coins (1971–81) all read "NEW PENCE" and are common at face value. The error is specifically the 1983 specimen reading "NEW PENCE".

2008 Undated 20p ("Mule")

The most famous and most findable UK error. The 2008 redesign of the 20p moved the date from the reverse to the obverse. During the die-set transition, a small batch was struck pairing a 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.

Realised prices: £50–£100 for circulated specimens; £100–£200 for UNC.
How to identify: a 2008 20p with NO year visible on either side. Both pre-2008 (date on reverse) and 2008-onwards (date on obverse, "TWENTY PENCE" reverse) are normal; the error has neither.
Beware: heavy circulation wear can obscure a date that is actually present. Check carefully under magnification before assuming it's an error.

1971 / 1972 New Pence on Wrong Planchets

During the immediate post-decimalisation period the Royal Mint occasionally struck a new-decimal die on a planchet of the wrong denomination. The most common variant is a 2p design struck on a half-penny blank (smaller diameter, lower weight). Strictly very rare; specimens command £500+ when authenticated.

2014–2017 £2 Inverted-Effigy / Die-Rotation Errors

A small population of bimetallic £2 coins from this period were struck with the dies misaligned by approximately 180°, so flipping the coin top-to-bottom shows the reverse upside-down rather than upright. Specific years with documented incidents include 2015 (Magna Carta and Royal Navy £2) and 2016 (Shakespeare).

Realised prices: £30–£100 depending on year, severity and condition.
How to identify: hold the coin obverse-up, then rotate it top-over-bottom. Reverse should appear right-way-up. If it's upside-down, it's an inverted-effigy error.

Missing Edge Inscription on £2 Coins

The bimetallic £2 coin is a three-step process: outer ring + inner core + edge inscription. Occasionally the edge-inscription step is skipped, producing a £2 coin with a smooth or generic reeded edge instead of the engraved legend (e.g. "STANDING ON THE SHOULDERS OF GIANTS").

Realised prices: £25–£75 depending on year. Newton-edge errors fetch the upper end.
How to identify: edge should carry text raised in relief, not punched in or absent.

2018 RAF "Lightning Bolt" 50p Off-Centre Strikes

A small population of the 2018 RAF Centenary 50p (Lightning II reverse) were struck with the design visibly off-centre by 5–15%. The number affected is unknown but specimens turn up regularly on secondary markets.

Realised prices: £15–£40 depending on severity.

Brockages and Die Caps

A brockage occurs when a struck coin sticks to the upper die and then strikes the next planchet, leaving the next coin with the design twice (or a mirror image). A die cap is the same situation but where the stuck coin remains on the die for many strikes, becoming progressively more cup-shaped. Both are extreme rarities for British coinage; specimens at auction realise £500–£3,000 depending on definition and condition.

Wrong-Date Variants

Occasionally a die for one year is reused for a coin meant to be a different year, producing a coin with the wrong date. The most famous British example is the 1962 to 1972 transition coins where some pre-decimal threepence dies remained in use briefly post-decimalisation. These are mostly numismatic curiosities rather than circulating finds.

How to identify an error coin

The five-step home authentication checklist:

Look it up first. Search our catalogue or the Royal Mint Museum archive for the same year and denomination. Confirm what the "normal" coin should look like. Many "errors" turn out to be normal variants.
Weight and dimensions. Use a calibrated jewellery scale (0.01 g resolution) and a calliper. Wrong-planchet errors will show clear weight and diameter differences. The Royal Mint publishes the spec for every modern issue.
Edge. £2 coins should have a raised text legend; £1 coins (12-sided post-2017) should have alternating smooth and milled segments; everything else has a milled or plain edge per its design.
Strike. Errors leave the rest of the coin looking normal — sharp details, even surface, clean edge. If the rest of the coin looks beat up, it's damage, not an error.
Photograph and compare. Take photographs in even, raking light. Compare to known specimens online. If still uncertain, send to a grading service.

Authentication and grading services

For any error you think is worth more than £100, professional authentication adds significant resale value and removes counterfeit risk for the buyer. The major options:

CGS UK — British, lower fees, faster turnaround. Recognised by UK auction houses.
NGC — American, second-largest globally. Strong on UK errors specifically.
PCGS — American, the largest global grading service. Premium pricing.

Fees are typically £20–£50 per coin. A slabbed authenticated error sells for 30–50% more than a raw equivalent, mostly because eBay buyers refuse to pay top prices for unverified errors after several years of fake-error scams.

Common error counterfeits to watch for

The error coin market attracts fakes. Watch out for:

Filed-off date 20ps. Genuine 2008 undated mules have a clean strike with no date present anywhere; counterfeits often show file marks where the date used to be on a normal 2008-onwards coin.
Cleaned and polished "uncirculated" 1983 New Pence 2ps. The 1983 error was struck only in proof sets, so any 1983 "New Pence" 2p that has clearly circulated isn't the error coin you're thinking of (though it may still be a curiosity).
Glued or repaired mules. Particularly on £2 bimetallics, where outer rings can be reattached after splitting. Authentication catches these.
Modern restrikes labelled as errors. Some private mints sell deliberately-erroneous modern strikings as "errors" — these are not Royal Mint errors and have no numismatic value.

Featured British error coins on MyCoinage

50 Pence - Elizabeth II 4th portrait; Christopher Ironside

2013

up to £1,800

50 Pence - Elizabeth II 5th Portrait; Peter Rabbit

2020

up to £1,480

50 Pence - Elizabeth II Kew Gardens; Silver Proof

2009

up to £568

50 Pence - Charles III Concorde; Silver Piedfort

2026

up to £267

50 Pence - Elizabeth II Peter Rabbit; Silver Proof

2016

up to £261

50 Pence - Elizabeth II 4th portrait; Athletics

2009

up to £256

Search the full catalogue →

Frequently asked questions

What counts as a "coin error"?

A mint error is any deviation from the intended design or strike that occurred at the Royal Mint itself, before the coin entered circulation. This includes dateless strikes, mis-pairings of dies (mules), off-centre strikes, double-strikes, inverted effigies, wrong-planchet strikes and missing elements. Post-mint damage is not a genuine error and has no numismatic premium.

How do I tell a real error from damage?

True errors carry the characteristic smoothness and uniform strike of a normal coin; the "error" is in the design itself, not physical trauma. Damage (scratches, gouges, corrosion, chemical etching) is easy to spot as it disrupts the designed surfaces. Professional grading from PCGS or NGC is the gold standard for authentication on any error worth more than £100.

Which UK coin error is worth the most?

The 1983 "New Pence" two-pence error is the most valuable widely-known UK error. Royal Mint proof sets that year were accidentally struck using the obsolete 1971–81 "New Pence" reverse die instead of the new "Two Pence" wording. Sets containing the error sell for £500–£1,500; loose specimens up to £1,200 in PR-65. The 2008 undated 20p mule is more famous but trades at a lower £50–£100 because around 250,000 entered circulation.

How many 2008 undated 20p coins were struck?

The Royal Mint has not given a definitive figure but estimates from numismatic experts and dealers put it between 50,000 and 250,000. The error happened when a die-update transition was botched: the 2008 redesign moved the date from the reverse to the obverse, but a small batch was struck pairing the new (dateless) reverse with the old (dateless) obverse. Result: a perfectly struck 20p with no date anywhere on the coin. They were released into circulation undetected and only spotted later by a coin-collector. The Royal Mint has confirmed they remain legal tender.

What is a "mule" coin?

In numismatics a mule is a coin struck from two dies that were never meant to be paired — for example, the obverse of one denomination and the reverse of another, or two reverses, or two different design generations of the same denomination. The 2008 undated 20p is a mule (new reverse + old obverse). Mules are almost always rare because they're the result of die-handling mistakes, not deliberate production. Confirmed mules typically realise four to six figures at auction.

Are off-centre strikes valuable?

Off-centre strikes (where the die wasn't aligned over the planchet during striking) range from minor (5–10% off) to dramatic (20%+ off, with parts of the design missing entirely). Minor off-centres on common coins are worth a small premium (£5–£25). Dramatic off-centres on circulating coinage can sell for £50–£300 depending on visual impact and the coin's normal value. Patterns and proofs that show off-centre strikes are exceptional rarities and command much more.

What is an "inverted effigy" error?

Most British coins are struck "medal alignment", meaning if you flip the coin top-to-bottom the obverse and reverse appear the right way up. An inverted-effigy or die-rotation error happens when the dies are mounted at the wrong rotation, so flipping the coin presents the reverse upside-down. Slight misalignments (less than 30°) are usually ignored; a full 180° rotation is a clear error. Particularly notable on £2 coins from 2014–2017, where loose-die incidents during a Royal Mint equipment change produced detectable rotations.

Should I get error coins authenticated?

For anything you suspect is worth more than £100, yes. Send to CGS UK, PCGS or NGC. Costs are typically £20–£50 per coin and the slab adds significant resale value because errors are widely faked. eBay buyers will pay 30–50% more for a slabbed authenticated error than a raw one.

Can a worn or damaged error coin still be valuable?

Errors retain most of their premium even at low grades because the rarity is in the strike, not the condition. A circulated 1983 "New Pence" 2p in Fine grade still trades at £200–£400; a heavily-worn 2008 undated 20p still £30–£50. Genuinely damaged coins (dropped, drilled, cleaned) lose most of their numismatic value regardless of error status, but normal circulation wear doesn't.

What should I do if I find an error coin in my change?

Stop touching the surfaces — pick it up by the edge and put it in a flip or 2x2 holder. Photograph both sides clearly with even lighting. Search our catalogue for similar issues to confirm what you have. If it looks like a real error, send to a grading service before listing. Do NOT clean it; do NOT polish it; do NOT try to "improve" it. Original surfaces are most of the value.

Are the Royal Mint required to buy back error coins?

No. Error coins are legal tender (you can spend them at face value) but the Royal Mint does not run a buyback or recall programme for issued errors. You sell them on the secondary market: eBay, coin fairs, specialist dealers (Spink, Baldwin's) or auction. The Royal Mint occasionally comments publicly on famous errors but otherwise treats them as legitimate issued currency.

Are there any error coins I should ignore?

Yes — "errors" that are actually deliberate design variants, post-mint damage or counterfeit fakes. Famous examples: misaligned design elements that are actually a normal die-pair tolerance (the £1 inverted-effigy myth, where many coins were never actually inverted), die-cracks that are normal late-die wear, and "blank planchets" that are usually just stripped or worn coins. Verify before buying.