The Oyster card system was down for at least five hours on Saturday, meaning gates on the London Underground were open and bus drivers could not take fares.

And cards used during that period got corrupted or incurred a fine, prompting Transport for London (TfL) to draft in extra 150 staff to hand out replacement cards on Monday morning to help prevent queues building up as 40,000 passes stopped working as a consequence of the fault.

“Anyone who touched in or out on Saturday morning has probably had their Oyster card disabled (code 30) and will need to change their Oyster card at a ticket office using the failed Oyster card procedure. If it is a student, child card etc, then they will need to contact Oyster for a replacement. Even our staff have had their passes disabled,” TfL said in a statement released yesterday.

The glitch has now been fixed and cards are now being accepted across the London Underground, DLR, overground and on the train services that accept Oyster, though a number of buses may still be facing problems.

All passengers affected by the problem will be given an automatic refund from Tuesday and will be able to travel even on services with faulty readers.

TfL is investigating the cause of the problem and should release a further statement later in the week.

“The vast majority of passengers have travelled without any disruption this morning and London Underground staff have minimised the delay to passengers with cards that are not working," said a TfL spokesman.

“Less than 1% of the 6 million regular Oyster card users required replacement cards after the incident on Saturday morning. We are replacing affected cards and there are now less than 35,000 cards that need to be replaced. If this has not been practical during this morning, London Underground staff, and London bus drivers, have allowed these passengers to travel," he said.

“Ticket offices are well stocked and we advise those passengers who have not yet replaced their cards to go to their nearest London Underground ticket office through-out today.”