Minor British Institutions: The 50 pence piece

British design tends to the sturdy rather than stylish. Things like red buses, telephone boxes and the JCB do not excite wows from besilked Italians or cool Swedes.

Occasionally, we surprise ourselves, and everybody else: the Tube map, the odd car, Cary Grant. Familiarity, though, has obscured the claims of the 50p, a remarkable thing.

It's an equilateral curve heptagon, a distinguishing, mysterious shape which, although it's not a circle, has the same diameter wherever measured, and is thus readable by slot machines.

It was the suggestion of H G Conway, the technical member of the Decimal Currency Board, charged with the change 40 years ago.

Conway has been little lauded, possibly because he was from Canada. The 50p ran into opposition, including the splendidly named Anti-Heptagonists, founded by a retired colonel who thought the coin "an insult to our Queen".

I don't know what happened to them; the 50p survives, though (since 1997) smaller. And it can roll, too.