LU says engineers are working flat out to rectify the line's problems

Alistair Darling told BBC London that testing the modified trains was taking far longer than anyone had expected but that safety was "paramount".

More than 30 passengers were hurt when a train came off the tracks at Chancery Lane station in January.

Mr Darling said he met LU managing director Paul Godier on Wednesday and was told trains would again be tested on the line on Thursday morning.

If they get the all clear from engineers and health and safety inspectors, then a limited service could begin on the eastern end of the line.

"We've got to make sure that safety is paramount," he told BBC London.

One train tested successfully

"We've got to make sure these repairs work. It has taken far longer than I or anybody else would have wanted."

Earlier this month one of the trains modified since the accident successfully travelled the length of the line and back in a strictly-supervised run.

But LU said it still could not give a date for any return of services.

The Central Line, which runs from West Ruislip in west London to Epping in Essex, has been shut for six weeks.

Limited service only

The service will be restarted between Bethnal Green and Woodford and if successful it will be extended to Loughton and then Epping.

LU says if the trains are not overcrowded the west side of the line from Ealing Broadway to Marble Arch will then be opened.

There are currently no plans to introduce the service on the far west of the line to West Ruislip, or the central section where the derailment happened.