The oyster smartcard system used on London's transport network broke down again this morning.

Ticket barriers were left open at all stations during rush hour as staff tried to fix the problem. The incident comes two weeks after a fault left 40,000 customers with corrupted cards after they touched in or touched out during a certain time period.

Transport for London says the problemonly affected pay-as-you-go cards, but barriers were been left open to aid the flow of people.

As of 10.30am, the problem was fixed and readers were progressively coming back online.

Cards were not corrupted in this instance, and a refund will be given to all customers charged the maximum £4 fare for journeys.

Oysters on buses, trams and the Docklands Light Railway were not affected.

"There was a technical problem with the readers," said a spokesman. "We believe that this problem, like the last one, resulted from incorrect data tables being sent out by our contractor, Transys."