TRANSPORT for London (TfL) is adjusting its clocks after it was revealed Londoners could have been overcharged for off-peak tube journeys.

Faulty clocks across the tube network could mean that off-peak travellers using Oyster pay-as-you-go have been charged peak rate fares.

The problem occurred when gate clocks were not fully synchronised with TfL's central clock.

A TfL spokesperson admitted they did not know which stations had been affected and that the problem could have existed since Oyster's introduction in 2003.

He said: "In theory, all gates could be affected. We estimate the proportion of customers affected could potentially be 500 people out of the 3million that travel every day.

We estimate the proportion of customers affected could potentially be 500 people out of the 3million that travel every day.

"We are working towards sychronisation but, as a temporary measure, there will be a four-minute window.

"The technology in the ticket gatelines, some of which are now 20 years old, is being upgraded as part of Transport for London's £10bn investment programme."

Peak times on the tubes run from 7am until 10am.

TfL has pledged the problem will be resolved by Friday and is offering refunds to anyone who thinks they may have been overcharged.

Anyone who may have been affected can telephone the Oyster Helpline on 0845 3309876.