Bronze 20p (1987)

Only a handful of these coins are known, so a confirmed example is priced on its rarity far more than on its grade. Proof of authenticity is what moves the value: a coin backed by a Royal Mint Museum test is a different proposition from an untested brown 20p, which may simply be a plated or discoloured normal coin worth face value. The date matters less than that evidence, since each of the known coins is effectively a one-off.

No circulation mintage has been published for the Bronze 20p, so it has no rarity rank.

A genuine bronze 20p shows the crowned rose reverse and a normal 20p heads side, but the whole coin is bronze in colour and noticeably thinner than a standard 20p. On the 1990 coin only three of the seven sides are fully formed and the rest of the edge is rounded, because the round blank was too small to fill the 20p collar. Colour alone proves nothing: the known coins were accepted only after their metal was tested.

The design on this coin is the familiar one: William Gardner's crowned Tudor double rose, with TWENTY PENCE and the date either side and the numeral 20 below, as used on 20ps from 1982 to 2008. What makes it an error is the metal. A bronze blank found its way into a press fitted with 20p dies and was struck as a 20p instead of becoming the coin it was made for. Accounts differ on where that blank came from. The bronze blanks were meant for other coins struck at the Mint, either a 1p or one of the overseas coinages it makes. The Museum confirmed the coins it examined by X-ray fluorescence, a test of the metal itself that ruled out plating or a surface stain. A coin dated 1987 was confirmed in November 2017, and a 1990 coin, found in a bank bag of 20ps in 1994, has also been verified. A 1984 date has been reported too, and a 1983 coin sold in 2026 with a Royal Mint Museum letter authenticating it. The 1987 and 1990 coins carry Raphael Maklouf's portrait of the Queen.