Track at the time of the Potters Bar crash has been condemned as "appalling" by Transport Secretary Alistair Darling after the publication of a damning new report into the accident.

The second interim study into the disaster that killed seven people concluded up to 20% of nuts on nearby sets of points were not fully tightened at the time.

Track sabotage has again been ruled out

Mr Darling said there must be a single point of responsibility for safety, instead of the current "blurred lines" between Railtrack, its contractors and subcontractors.

He told BBC News: "The approach that Railtrack took when the industry was privatised in the early 1990s, which was to contract out not only maintenance but key decision about what should be maintained, does not work.

"The state of the points at Potters Bar was clearly appalling."

He said Network Rail - the body taking over from Railtrack - would make sure contractors carried out work properly.

	:	The points failure
Click above to see how the train derailed

Bereaved families have again called for a full public inquiry into the 10 May crash.

The second Health and Safety Executive report confirmed that the set of points the train rode over before the accident - designated 2182A - had a set of nuts missing and "failed catastrophically".

But it also showed that 20% of other points in the area had nuts that were "not fully tight".

It said there was no evidence to back claims by maintenance contractor Jarvis that sabotage could be the cause of the problems, although it was keeping an "open mind".

Jarvis said later it still thought the points could have suffered "technical interference".

Inquiry call

The HSE recommended that Railtrack and its contractors should review the design, maintenance and checking of points.

Railtrack said it was already looking at improving the way maintenance was carried out.

Chief executive John Armitt told BBC News: "There has been a terrible accident at Potters Bar, but that was an isolated incident and one from which we must learn all the lessons that we possibly can."

Writer Nina Bawden whose husband Austen Kark, 75, died in the crash, said the crash was not a one-off, and there should be a public inquiry to ensure rail travel was safe.

"It is now clear that... the danger of a derailment from loose lock nuts on points is one which exists around the country."

Mick Rix, general secretary of train drivers' union Aslef, said senior management at Jarvis should be prosecuted for failing to ensure rail safety.

Ongoing HSE inquires are focusing on:

Inspection and maintenance of points 2182A Training and competency of relevant workers The management of records about points 2182A

Jarvis said the state of the Potters Bar points had been "unique", and pointed out that forensic tests on the points were still ongoing, and may still find sabotage to blame.

It said the so-called "loose" nuts found by the HSE still had to be removed with a spanner, and added there was "no evidence" that the crash was the result of maintenance failure.

Seven people died and dozens were injured when the King's Cross to King's Lynn passenger service came off the tracks as it passed over the main faulty points.

Mystery workers

The HSE said much of its detailed findings could not yet be revealed as this may jeopardise the ongoing British Transport Police-led investigation.

BTP said its inquiry was focusing on the maintenance and management of the track in the area.

It was still trying to trace five "mystery" workers wearing orange jackets, seen on the track hours before the crash.

Mr Darling confirmed earlier this week that a new body would be set up to replace the HSE in investigating train crashes.

That followed criticism by victims of the Potters Bar crash over the speed and efficiency of the HSE's investigations, and queries about its dual role in regulating and investigating the railways.