A care home manager has been ordered by a judge to pay a total of £1,118.62 after he tried to settle an £804 debt to his accountant with five crates of mostly 1p and 2p coins. He had been to the bank especially, he said: be glad that you weren't behind him in the queue. So what did Robert Fitzpatrick, the care home manager, do wrong?

This might come as a surprise, but according to the Royal Mint, 1p and 2p coins are legal tender only if you are paying for something costing 20p or less: once you have amassed 21 or more 1p pieces, your coins contravene the Coinage Act 1971 if used in a single transaction. Even if you are buying penny sweets.

You can spend up to £5 in 5p or 10p coins, or up to £10 each in 50p and 20p pieces. Pound coins are legal tender for any amount, offering the chance for a frisson of defiance while staying on the right side of the law.

So Mr Fitzpatrick should have paid with 774 £1 coins, 20 50p pieces, 50 20p pieces, 50 10p pieces and 100 5p pieces. Counting that lot would still be pretty annoying.

• This article was amended on 16 May 2012. The original said the man was fined for attempting to pay a large bill with 1p and 2p coins. He was sued and ordered to pay a total of £1,118.62, including interest. The original headline referred to a tax bill, when it was an accountant's bill.