Transport for London (TfL) is hoarding more than £321 million in unused Oyster card money.

Figures from the transport body showed that the money applies to balances and deposits on Oyster cards that have not been used for at least a year.

Liberal Democrat London Assembly member, Caroline Pidgeon said the “staggering” rise of dormant cards was creating an “immense cash mountain” for TfL.

Ms Pidgeon said: “TfL never stops bombarding us with advertisements and information campaigns but highlighting this cash mountain is one issue that they remain incredibly quiet about.

“It is time TfL devoted far more time and energy telling the public how they can get their own money back.”

The Liberal Democrat politician also said that a weekly cap on Oyster promised by previous Mayor Boris Johnson in 2015 needs to be introduced “as quickly as possible”.

TfL’s chief technology officer, Shashi Verma said: “We’re committed to ensuring that our customers can get back the credit on their Oyster cards if that is what they want.”

The credit on an Oyster card never expires and unused credit can be claimed back from any Tube station ticket machine.

Since the launch of Oyster card 15 years ago more than 100 million people have used the cards.

The card system costs TfL millions a year to administer, while contactless payments are run by banks.