A broken rail was the "substantial" if not only cause of the Hatfield train crash, a preliminary Health and Safety Executive report has found.

The investigation into Tuesday's accident - which killed four people and injured more than 30 others - has ruled nothing out, according to HSE chief railway inspector Vic Coleman.

I have safety as priority one, priority two and priority three

John Prescott

"But on the basis of what we know so far we have found no evidence that the signalling or the train, defects in the train, are part of the initial causation of this accident," he said.

"We have observed some track defects and these are significant and it is clear that a track defect is certainly a substantial cause of this accident, if not the only cause."

Track closures considered

Deputy Prime Minister John Prescott insisted on Friday that Railtrack reveal what steps it is taking to identify faulty tracks.

He said it was obvious the company had not met its commitments on track repairs, but said he was willing to listen to requests for help.

Relatives of the victims visited the Hatfield crash site on Friday

"They had better come and tell me what changes are necessary to get a higher level of safety. I have safety as priority one, priority two and priority three," he told the BBC.

Mr Coleman said if the HSE was shown evidence of public safety being endangered, it would consider ordering the closure of sections of track.

The GNER passenger train, heading from London to Leeds, was travelling at around 115mph when it crashed 17 miles into its journey.

The damaged rail thought to have sparked the tragedy will be examined to establish why it failed.

A specific type of metal fatigue is thought to be the most likely cause.

Appeal dropped

The phenomenon has been seen elsewhere in Europe but has only been recognised in the last two years.

Mr Coleman said the most serious damage to the train was caused by carriages smashing into trackside steel poles carrying overhead electric cables.

Vic Coleman stressed the findings were preliminary

In a further development, Railtrack has dropped its appeal against a �40m fine for failing to meet performance targets, saying it would be inappropriate in the wake of the Hatfield disaster.

The company's lawyers were set to use the Human Rights Act to argue that the fine was too high - despite last year's pre-tax profits of �428m - in the High Court on Monday.

The fine was imposed in January by Rail Regulator Tom Winsor on a basis of �4m for each percentage point by which Railtrack failed to meet his target for train delays.

Major risk

Railtrack has also admitted warning its maintenance company, Balfour Beatty, seven months ago there was a major derailment risk in the Hatfield area.

Mr Coleman said it would now be "absolutely crucial" for the investigation to look at decisions taken after that warning.

"That's a key question, could more have been done than in fact was done?" he added.

Both the HSE and British Transport Police could bring prosecutions if breaches of regulations or negligence were found.

A broken rail has also been implicated by a preliminary HSE investigation into the derailment of a passenger train at Stafford on Thursday, which caused minor injuries among the 80 passengers.