Rail maintenance workers repeatedly warned Railtrack managers of flooding and metal fatigue on the fatal stretch of line near Potters Bar.
Bob Crow, head of the National Union of Rail, Maritime and Transport Workers Union, told The Independent on Sunday that nothing was done about the warnings.
He said vibrations caused by wear and tear, or subsidence, could ultimately have led to the crash by loosening bolts in the points which caused them to change when the 12.45 from King's Cross to King's Lynn travelled over them at 100mph.
Senior investigators at the scene of the crash confirmed yesterday that the set of points, no 2182, did fail – causing the fifth fatal rail accident in five years.
Suspicion turned to the points after early reports of an object on the line proved wrong. The points should have been clamped open, but appear to have switched as the train passed over. Pictures from the scene seem to indicate that the points are open – pointing away from the main line.
The first three carriages passed over safely, but the wheels of the fourth and last carriage became snagged as the points changed. This forced the last carriage violently to the left, breaking the wheels off and separating the carriage from the train. While the train continued upright to come to a halt 500 yards beyond the station, the final carriage jack-knifed across the track, and skidded sideways along to the station.
Bob Crow alleged that the points had not been properly serviced since January, when they should be done every six weeks. "It is a long period between January and May," Mr Crow said. "The company standard is that they should be done every six weeks. We believe the line should be inspected every day. My members have been complaining about the whole line to Hatfield suffering from metal fatigue and flooding. Nothing has been done about it."
Railtrack yesterday defended its safety record since the Hatfield disaster 14 months ago, and that points 2182 had been checked recently. It had also checked nearly 400 sets of points across the UK in the 24 hours since the Potters Bar crash. But none of them had shown any similar problems. The points checked were a sample of all the points on the rail network, but a spokeswoman said: "We're confident that none of those had similarities with the one at Potters Bar."
Forty officers from the British Transport Police carried out a fingertip search of the site in the hunt for clues. Inspector Philip Trendall said officers were looking for any fragments which might explain why the train derailed.
He confirmed that crash investigators were studying a set of points which could be to blame. It is thought that the points changed as the third or fourth carriage of the four-car train passed over them. This separated the last carriage from the train, flinging it sideways. It also explains why the last carriage jack-knifed.
An object placed on the line by vandals is unlikely because the first three carriages remained upright. And a broken rail, the cause of the Hatfield crash, has been ruled out because the Potters Bar site is not as strewn with debris as Hatfield was.
Investigators, who hope to be able to publish a preliminary report next week, will be trying to find out why the points changed as a train is travelling over them. The train was not due to stop at Potters Bar and the points would have been clamped open. The clamps are sturdy and can be moved only with an electrical charge. Mr Crow said it is unlikely flooding could have caused an electrical fault or that human error was the cause. Other theories emerging were that an object fell off the train, ruled out by Mr Crow, or that a cracked wheel snagged on the points.
Responsibility for maintaining the carriages is divided between WAGN, which leases the stock, and Bombardier, which built it. A WAGN spokesman said the carriages involved in the accident were "only a couple of years old" and were regularly maintained. "They are checked every 21,000 miles," he said, "which is the equivalent of about once every 21 days."Reuse content