Missing parts on a railway switching point caused a high-speed train crash on Friday which killed seven people and injured around 90 others, the head of Britain's rail network said today.
Mr John Armitt, chief executive of Railtrack said he could not say why vital nuts were missing from bolts in the system, but insisted it had been checked just the day before the accident.
"The fundamental fact that we've been able to establish so far is that there were nuts missing from key bolts in the points structure," Mr Armitt said.
Safety experts investigating the crash blamed the faulty points system for derailing a passenger train just moments before it was due to pass through Potters Bar station, north of London, on Friday at lunchtime.
The train was travelling at 100 mph (160 kph) when the wheels of its rear carriage came off the track. Witnesses said they heard a deafening bang and saw passengers flung out of windows as part of the four-carriage train hurtled into the station's platforms, partially demolishing a bridge.
Britain's Observernewspaper said on Sunday that senior rail industry sources said the nuts on the points had been removed deliberately in a "sophisticated" act of vandalism.
But both Mr Armitt and British Transport Secretary Mr Stephen Byers said it was too early to say how the nuts became detached.
Many of the around 90 people injured in the crash were described as "walking wounded", but five people were still in hospital today.
The derailment was less than five miles (eight km) from Hatfield, where a broken rail caused an express train to come off the tracks in October 2000, killing four people.
The accident was the latest in a series of tragedies to hit Britain's railways since they were privatised by the Conservative government of Prime Minister John Major in 1996.
Seven were killed in a crash in the London suburb of Southall in 1997 and in October 1999, 31 people died in a collision at Paddington in west London. Ten died in February 2001 in an accident at Selby in Yorkshire, northern England.