Rail company Thameslink was battling to get services back to near-normal this afternoon after most of its fleet got stuck in the sidings.

A power failure caused major disruption this morning as passengers crammed on to other operators' services.

Passengers' group Brighton Line Commuters questioned whether poor track maintenance was to blame.

Almost all Thameslink trains were stuck in sidings south of Bedford when a points and signal failure knocked out ten miles of track.

It meant virtually no Thameslink cross-London service between Brighton and Bedford.

Commuters had to crowd onto South Central and Virgin services and change at Victoria and Clapham Junction to get to the City of London.

To add to the turmoil, services were delayed as travellers packed on to trains.

The electricity supply failure was discovered at 4.30am as the first trains were about to leave the sidings.

The trains could not get into Bedford - the start of their journey to Sussex - for six hours.

Shelley Atlas, chairwoman of Brighton Line Commuters, said: "The cancellation of the early morning Thameslink trains meant passengers had to crowd on to South Central services.

"Trains got more and more crowded up the line as the rush hour continued.

"Railtrack and Thameslink must ensure this does not happened again. Was poor maintenance of the track to blame?"

Thameslink spokesman Martin Walter said: "We started to run again at just after 11am, but it will take us some time to get back to normal because our trains are in the wrong position.

"We do not know the cause of the problem. It would appear to be a Railtrack matter.

"We apologise to all our customers who were delayed by this problem.

"We are concentrating at the moment on getting our trains back to normal running. We will later look at the causes."