London Underground is investigating the cause of a computer glitch that caused its Oyster smartcard ticketing system to crash during the peak rush hour this morning.
Ticket gates had to be left open when Oyster card readers at tube stations across the whole of London Underground and the Docklands Light Railway crashed at 0400.
Transys, the EDS-led consortium behind the Oyster card system, said it had identified the problem by 0830 and that most of the readers were working again by mid-morning.
A spokeswoman for Transys explained that information on lost and stolen Oyster cards that have been stopped overnight is sent to the card reader network at 0400 every day.
On this occasion the data appears to have caused the readers to crash and while the problem has now been fixed Transys is still investigating why it happened.
"We are now looking at what caused it so we can make sure it doesn't happen again," she said.
Oyster cards were introduced in 2003 with the £1.2bn PFI contract going to the EDS-led Transys consortium, which also includes Cubic Transportation Systems. The smartcards are manufactured by Giesecke & Devrient and SchlumbergerSema using MiFare chips from Philips Semiconductors.