"Pay-as-you-go Oyster cards do not expire and customers are able to return their cards at any time for a refund of the remaining balance and card deposit," Transport for London said. "Revenue generated from fares, including Oyster fares, is used to operate, maintain and upgrade London's transport network.

How long are Oyster cards valid for?

The pre-pay money loaded on an Oyster card is valid as long as the card is used at least once every 24 months. If it's not been used during that amount of time the money can be refunded by returning the card to Transport for London - info at the website.

How do I know if my Oyster card is expired?

There is no expiry date on Oyster cards.