A new report says poorly maintained points were the most likely cause of the Potters Bar rail crash.
The fourth carriage ended up under the platform canopy
Seven people died and 76 were injured when the train derailed just outside the station on 10 May last year as it headed to King's Lynn, Norfolk.
The Health and Safety Executive's third progress report found no evidence that sabotage or vandalism was behind the derailment.
Agnes Quinlivan, 80
Austen Kark, 75
Jonael Schickler, 25
Emma Knights, 29
Chia-hsin Lin, 29
Chia-Ching Wu, 30
Alexander Ogonwusi, 42
It believes the crash happened because nuts on a vital set of points were missing, and other parts were in poor condition, causing the points to fail catastrophically and the train to derail.
When the rear wheels of the third coach were travelling over the points, the wheels on each axle were forced in two opposing directions, derailing the rear of the third coach and the fourth coach entirely, the report said.
"Other sets of points in the Potters Bar area were found to have similar, though less serious, maintenance deficiencies, indicating a wider problem."
The engineering firm Jarvis, which had responsibility for track maintenance in the area, has always insisted that sabotage could not be ruled out.
Lack of guidance
In examining the management of the points, the HSE said there appeared to be "no guidance or instructions
for setting up, inspection or maintenance" of the points.
An investigation board which oversaw the inquiry concluded: "The investigations so far show that the most likely underlying cause of the derailment was the poor condition of points 2182A at the time of the incident."
It said insufficient maintenance "probably arose from a failure to understand fully the design and safety requirements" of the points.
It also highlighted a lack of response to reports of a "rough ride" in the area south of Potters Bar station the night before the accident.
Perdita Kark, whose father Austen was killed in the crash, said the report "confirms what we already knew".
"Of course, it was not sabotage.
"It was not a one-off. There is dramatic evidence of poor maintenance and bad management across the rail network. And this could very easily happen again."
Relatives and victims' lawyer Louise Christian said it was vital that the government called an immediate public inquiry into the crash.
"The great worry is that while nobody accepts responsibility not enough is being done to put things right," she said.
"The report demonstrates in graphic
terms that a decaying rail infrastructure with damaged safety-critical parts is not subject to proper monitoring, maintenance or replacement."
Jarvis said the points were maintained in accordance with long-established industry procedures by trained and competent staff.
The company said the points were formally inspected jointly by Railtrack and Jarvis seven weeks before the derailment and found to be in good condition.
"The investigation has yet to establish what happened in the seven weeks between the inspection and May 10.
"Therefore it is still uncertain as to what happened to cause the points to fail so catastrophically."
The Transport Secretary, Alistair Darling, said the findings justified the government's decision to replace Railtrack with a not-for-profit company, Network Rail, with overall responsibility for track maintenance.
A police investigation into the incident is continuing.