Rail passengers today faced delays after speed limits were imposed on potentially dangerous tracks.

Railtrack has identified 81 trouble spots across the network with "similar characteristics" to the track believed to have caused the Hatfield disaster.

They include the stretch of line between Three Bridges and Balcombe Tunnel on the main London-Brighton route.

The company has imposed "precautionary" speed restrictions - as low as 20mph in some places - which will cause widespread delays.

Railtrack bosses have vowed to make safety their top priority as it emerged the company knew the site of the Hatfield rail disaster was in a "grave" condition.

They admitted there were 81 spots on Britain's railways where the track featured "similar characteristics" to the one suspected of causing the Hatfield rail disaster, which claimed four lives.

A second train was derailed yesterday as Railtrack chiefs held emergency talks with train operating companies and contractors to review initial findings about the Hatfield disaster and to discuss safety.

Railtrack chief executive Gerald Corbett was back at his desk today - but facing mounting criticism of his company's stewardship of the railways.

The firm's board rejected Mr Corbett's resignation offer, made after the Hatfield rail crash which claimed four lives.

Sussex pilot Steve Arthur, 46, was one of four people killed in the disaster.

Mr Arthur, of Old Brighton Road, Pease Pottage, died in the buffet car of the Leeds-bound train on Tuesday.

His widow Lindsey, 33, told how her husband had been travelling to Leeds to pick up passengers and fly them to Jersey in a private jet.

A 60mph limit has been imposed between Three Bridges and Balcombe Tunnel - a reduction of at least a third.

The section has "similar characteristics" to the track believed to have caused the Hatfield disaster because it is on a bend and the same type of trains use it.

The speed restriction will say in force for several days while engineers inspect the track to assess whether repairs need to be carried out.

A Railtrack spokeswoman said: "Reducing speed is purely a precautionary measure which reduces the stress on the tracks. At the moment we do not know if this track has any problems."

Connex said the restrictions were only causing delays of several minutes at most.

This morning, Sussex commuters still seemed confident about the track's safety.

Tony West, of Fairford Road, Haywards Heath said: "I don't really have an option. One of the problems is that there is no London to Brighton line without going through the Balcombe Tunnel.

"I still think that the railway is the safest method of travel, even given what has happened. But they should make it safer."

Day tripper Jon Wilson, of Lewes Road, Haywards Heath, said: "It seems a sensible precaution. Maybe people will have to accept a little disruption to make sure they travel safely. That's more important. I still feel safer in a train than in a car."

Inquests have opened today into the deaths of the four Hatfield rail disaster victims.

They were Mr Steve Arthur, Robert Alcorn, 37, Peter Monkhouse, 50, and solicitor Leslie Gray, 43.

Coroner's officer Sergeant John Luck said Mr Arthur died from "multiple injuries, including head injuries".

The inquest was adjourned until 10am on November 21 in Hertford.

A full inquest could be severely delayed if a public inquiry is held.