A large-scale IT failure forced London Underground to shut a major commuter line for much of the day yesterday.

The Circle line was entirely closed during the morning rush hour, causing travel havoc for people working across central London and the City, after a computer problem occurred at Aldgate station in east London.

Other sections of the line remained closed for the rest of the day. Part of the Hammersmith & City Line was also suspended, between Moorgate and Barking.

Transport for London, which runs the Underground system, said the problem was linked to a “major computer failure”. A spokesperson was unable to state what technology was affected, or how it was fixed. The problems follow maintenance work over Easter, which was aimed at preparing for longer trains to use the tunnels.

Today, the Circle line continued to be suspended in one direction between Mansion House and Liverpool Street, with minor delays elsewhere due to a signal failure at Aldgate.

The spokesperson insisted today's problem was unrelated. But Howard Collins, London Underground's chief operating officer, told the Evening Standard newspaper yesterday evening that there would be some continued disruption “as works will be required overnight to repair the fault”.

Meanwhile, SAP-based TfL is preparing to sign an extensive range of framework agreements, totalling a potential £70 million and covering IT services. The services will be available to other high-profile local bodies, including the Greater London Authority, all London borough councils and the Metropolitan Police.