An Islington shopper could have bought the world’s most expensive birthday cards – after he was charged �250 each for three.

James Bertin was shocked when he discovered the mistake two days after purchasing the cards at Joy in Upper Street.

Having unwittingly paid �750 in all – 100 times the �7.50 value of the cards – he was pushed over his overdraft limit and had to wait days for the refund to clear.

Mr Bertin, 32, of Marlborough Road, Upper Holloway, who works for the Environment Agency, said: “It’s a bit ironic that the shop’s called Joy because I’ve not had a lot of it.”

The till has no display that gives the amount of purchases. The figure is only shown on the card machine.

A spokesman for Joy said: “We are extremely sorry for the mistake.” Joy refunded Mr Bertin the full amount the moment bosses realised what had happened. They have offered to cover any bank charges as well as giving him a gift voucher.