The coins have been dubbed the 'holy grail' of change collecting and if you find one it could be worth a lot more than 20p ...

An unusual coin could net its owner over 250 times its face value after an error when it was made. The rare 20p coin was one of an unknown number released by the Royal Mint without a date.

The vouchers will have instructions of how to use them on the back. Read the instructions carefully and ... All meters in London accept 20p and £1 coins. Pay & display machines will allow payment by a ...