I've got a rare £2 coin where the Queen is wearing a necklet. How much is it worth

A. £2. And it's not rare.

Q. Don't believe you.

A. Try going to see a coin dealer, then. You're likely to emerge with a black eye, too, for wasting their time.

It's an urban myth that seems to have originated from a local radio broadcast in 1997 where a phone-in caller said he'd heard the coin was worth £15. Hmm. Phone-in caller. Local radio station. Hardly bywords for accuracy, are they

All £2 coins from 1986 to 1997 bear the queen's third portrait, in which she is shown wearing what appears to be a pearl necklet. From 1998 the design changed to a more mature fourth portrait, in which the Queen is shown truncated at the neck rather than the shoulder. She therefore appears without a necklet.

Q. My friend's brother's got a 1933 penny - and I've seen it. You're not going to say that's worthless

A. It's almost certainly a forgery.

Q. How can you know

A. No pennies were minted in 1933 for circulation. Some were minted, though, as tests pieces. The Royal Mint was trying to solve the problems of 'ghosting', where a double image appeared, and continued to produce a number of experimental designs.

A small number of these were tested by striking pennies from experimental die designs. These were not intended for circulation and they were never issued. Some of these are single-sided, the opposite side remaining blank. Two such coins are held by the British Museum and another four in the Royal Mint's collection.

Q. So none got out

A. Three did - but they were well hidden.

Q. How

A. Three 1933 pennies supplied by the Mint to be placed under foundation stones of buildings: one under part of the University of London, two others under churches. One of the churches, at Middleton near Leeds, was damaged by thieves who managed to remove and steal the 1933 penny buried under its cornerstone. As a precaution, the other church removed its coin and sold it by auction in 1972.

Q. So the one I've seen is probably a forgery

A. Yes. On a number of them, the 5 has been changed to a 3 on a 1935 specimen. On others, the correct date has been ground off and the date sliced from another coin stuck on.

It also might have been a 1933 penny from Australia, British West Africa, Jersey, or Ireland. Sorry.

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Steve Cunningham