Why it pays to look closely at your change

Every day, millions of coins pass through British tills, pockets and purses. Most are perfectly ordinary. But among them, a small number carry mistakes made at the mint — errors that can turn a humble 50p or £2 into something worth many times its face value. You do not need a specialist collection to find them. You just need a keen eye and a little patience. The thrill of spotting an off-centre strike or a double die in your change is real, and it costs nothing to look.

Off-centre strikes: when the die misses the mark

An off-centre strike happens when the blank coin is not seated properly in the collar die. The hammer die comes down misaligned, leaving the design shifted to one side. The result is a coin with an uneven border — one side may show a sliver of blank metal, while the opposite edge has the design running off the rim. The further off-centre, the more valuable the coin. A 10% shift might be worth a few pounds; a 50% shift can fetch hundreds. To spot one, hold the coin at arm's length and check that the design is centred within the border beads. Then look at the rim — is it complete all the way around? A missing section of border or a flattened edge is a clue. Check both sides, as the error can affect one or both.

Missing mint marks: the blank that speaks volumes

Most UK circulating coins do not carry a mint mark, so a missing one is not usually an error. However, some special issues — particularly those struck for collectors or for overseas territories — do include a tiny mark, often a letter or symbol, near the date or below the bust. If that mark is absent because the die was filled with grease or polished away, the coin is an error. The same principle applies to missing designer's initials. For example, the initials "IRB" for Ian Rank-Broadley appear on many UK coins. If they are gone, that is a filled die error. These are subtle but can be valuable. Use a magnifying glass and compare your coin to a known example. A missing mint mark is a blank where there should be a mark — a quiet but significant flaw.

Double dies: the ghost in the die

A double die error occurs when the die itself is struck twice by the hub during manufacturing. The design on the die becomes doubled, and every coin struck from it shows the same doubling. You will see it most clearly on letters, numbers and the date — look for a ghostly second image, extra thickness, or notched serifs. The classic UK example is the 1971 2p with a doubled date, though many others exist. The doubling is not a scratch or wear; it is part of the coin's relief. Tilt the coin under a light and use a loupe. If the doubling is strong and obvious, the coin can be worth a premium. Minor doubling may add only a little, but it is still a fascinating find.

Other errors worth knowing

Beyond the three main types, a handful of other errors turn up in change. A mule is a coin struck with mismatched dies — the famous undated 20p from 2008 is a prime example, where the obverse and reverse dies were paired incorrectly. A wrong planchet error means a coin struck on a blank intended for a different denomination or metal, such as a silver-coloured 10p on a copper-nickel blank. A brockage shows a mirror image of the design on one side, caused when a struck coin sticks to the die and impresses its image onto the next blank. A cud is a blob of metal at the rim from a broken die. Clipped planchets, lamination errors and die clashes are also collectable. Each has its own charm and value.

How to check your change like a seasoned collector

Start with good lighting and a magnifying glass or a jeweller's loupe. Work through your change methodically: check the date, the lettering, the rim, and the overall centring. Weigh suspicious coins if you have accurate scales — a wrong planchet will be the wrong weight. Keep a small notebook or a phone note of known errors you are hunting. When you find something, do not clean it. Cleaning removes the natural patina and can destroy value. Store the coin in a paper or plastic flip, and handle it by the edges. Remember that most errors are minor and worth only a few pounds, but the rare major ones can be worth hundreds or even thousands. Get a second opinion from a coin dealer or club before selling. And above all, enjoy the hunt. Every handful of change is a small treasure hunt.