Transport for London has been urged to do more to help people reclaim unused money on Oyster cards after research showed the total had reached almost £170 million.

Caroline Pidgeon, leader of the Liberal Democrats on London Assembly, said the money left on the travel cards had not been used for over a year.

"When TfL's cash pile is growing by more than £2 million a month I simply do not accept that TfL are doing everything they reasonably can to allow the public to claim back their own money.

"Transport for London are never shy in using publicity except it seems when it involves telling the public how they can get back money left on dormant Oyster cards.

"It is time that TfL started to be far more active and gave more people the chance to get hold of their own money sitting on unused Oyster cards."

TfL's director of customer experience, Shashi Verma, said: "Credit on Oyster cards does not expire and customers can get a refund at any time they wish. Refunds can be obtained from any Tube station ticket machine or by contacting customer services on 0343 222 1234.

"We regularly contact customers and run extensive marketing campaigns to publicise how refunds for unwanted Oyster credit can be obtained and will do so again later this year.

"However, our research shows customers often want to keep their Oyster cards for future travel, when family and friends visit or even as a souvenir."