The firm in charge of maintaining the Potters Bar rail line says photographs support its claim that sabotage was the cause of the crash which killed seven.

The announcement from Jarvis came as trains began running through the Hertfordshire station for the first time since the disaster.

It also came on the day a new report claimed a 10-mile stretch of railway through Essex still had 30 faults which had been reported - but lie unfixed.

Jarvis's statement, made to the London Stock Exchange, said photographs taken of the points immediately after the accident showed that in addition to two sets of nuts having been removed, the inner nuts on the points had been adjusted in the 48 hours before the accident.

It is our belief ...that sabotage cannot be discounted

Jarvis statement

But the statement added: "No maintenance had been carried out on the points in the previous 48 hours."

In an interim report into the crash last week, the Health and Safety Executive (HSE) said the detached nuts probably caused the crash in which the last coach of a West Anglia Great Northern train derailed just outside Potters Bar.

But the HSE said it had not found any evidence of vandalism or deliberate damage - although neither could be ruled out.

Other rail industry experts have said the chances vandalism was to blame were "less than 1%".

The statement from Jarvis said: "It is our belief that it is too early to judge the ultimate cause of the accident, and that sabotage cannot be discounted."

Byers promised improvements in rail services

Monday's Daily Mirror featured photographs of railway track between London's Liverpool Street station and Colchester in Essex and claims to have found more than 30 faults.

The pictures were said to highlight problems ranging from a missing bolt to severe cracking of the type that caused the Hatfield rail crash.

An anonymous rail worker told the paper: "If you knew as much as I do about the state of the track, you'd think twice about taking the train."

'Rocket science'

Following the derailment on 10 May, the fourth coach of the WAGN train became stuck under the canopy of Potters Bar station. It was finally lifted clear last week.

The funeral of one of the seven victims, great grandmother and former district nurse, Agnes Quinlivan, takes place on Monday.

In an address to rail workers' union Aslef on Monday, Transport Secretary Stephen Byers promised big improvements to the way the rail network is maintained.

He told delegates he didn't want to pre-empt the findings of the inquiry into the Potter's Bar accident - but the time was right to look at the use of contractors and sub-contractors in carrying out repairs.

He said: "Running an effective and reliable railway service is not rocket science. It is done elsewhere in the world - it can be done here."

He added he believed putting Railtrack into administration was the right thing to do and he would have "done it again".