A motor fell off a carriage causing the derailment

The Central Line, the longest on the network, has been shut since one of its trains derailed and hit the station wall at Chancery Lane on 25 January.

An interim report published on Friday confirmed the crash was caused by a traction motor falling off the fifth carriage and onto the track - causing following carriages to derail.

We are hoping to have the Central Line back within weeks Bob Mason, London Underground

They still do not know why the motor fell off, but are fitting safety brackets to catch them before they hit the track should any more come loose.

The Waterloo and City Line, which uses the same design of train, was also closed and an estimated 600,000 commuters a day have been affected.

More than 80,000 compensation cheques have been sent out to commuters holding annual and monthly travelcards.

London Underground's director of stations Rob Mason told BBC London he heard commuters saying it would be September before the line opened.

"That is totally untrue," he said. "We are hoping to have the Central Line back within weeks, but certainly by April we are hoping to have the whole thing back in."

Loose bolts

The Waterloo and City Line opened again on Tuesday, but independent engineers were called in after loose bolts were discovered within eight hours.

The derailment is likely to land London Underground with a heavy bill, but Mr Mason said Tube fares would not rise as they are set by the mayor.

The Central Line has been shut for weeks

He said compensation was being issued to travelcard holders who usually used either line.

He said: "They can ring a number and there will be a cheque in the post coming back to them.

"Last week when I was in the office we were signing 80,000 cheques."

The report confirms that concerns about a problem on the train which crashed were received eight stations before the derailment happened.

When the driver reached St Paul's he was told to take the train, which was carrying around 750 people, out of service at Holborn - one station on from the crash at Chancery Lane.

Bobby Law, London organiser of the Rail, Maritime and Transport union. said: "The report does not address the communication breakdown on LU brought about by the fragmentation under part-privatisation."