Oyster card passengers at Sutton station were charged £132,000 for incomplete train journeys last year, according to new figures.

In 2010, 14m journeys in London saw passengers charged the £7.40 maximum fare for their journey, instead of the lower amount for the distance they travelled.

National rail customers have charged a total of £25.8m above the cost of their journey after Oyster card payments were extended to national rail stations in January last year.

Liberal Democrat London Assembly member Caroline Pidgeon said: “This level of overcharging is totally unacceptable.

“Of course in some cases passengers might forget to touch in and touch out, but such huge levels of overcharging clearly demonstrate there are some structural problems with how Oyster is operating.

“It is clear not enough is being done to ensure the machines and the technology are working properly.

“Transport for London need to take immediate steps to make it far easier for people to be able to claim a refund when they have been overcharged.

“Above all else, the levels of overcharging occurring need to be published at every station, so passengers are alerted to this serious problem.”

In a written response to Liberal Democrat questions, London Mayor Boris Johnson, said: “Maximum fares are not overcharges. The terms of pay as you go make it quite clear users must touch in and out to obtain the best fare.

“Maximum fares are charged to deter fraud and ensure users validate their cards properly.

“In principle, customers who do not touch in at the start of their journey are at risk of a maximum fare because they are travelling without a valid ticket.

“TfL calculates between 60 and 80 per cent of the revenue raised through maximum fares would have been spent by customers if their Oyster card were validated correctly.”

He said refunds were available from the Oyster help-line and London Underground stations, and £10m of maximum fares are refunded each year.