Investigators are due to publish their initial report into the Cumbria train crash which killed an 84-year-old woman and seriously injured eight others.
Rail expert Christian Wolmar told the BBC that it would reveal that part of a set of points to the south of the crash site was missing.
The stretcher bar, which keeps the rails apart, was not in place, he said.
The report is considering what caused the London to Glasgow Virgin Pendolino to derail near Kendal on Friday.
Mr Wolmar told BBC News 24 that his contacts had told him that as well as the missing stretcher bar, nuts and bolts had been found on the track.
It appeared to be a "terrible piece of maintenance", he said.
The stretcher bar was essential to keep the rails the right distance apart, Mr Wolmar said, and if it was missing the rail would be left "flapping about".
Meanwhile the grandchildren of the woman who died in the crash, Margaret Masson, have spoken of their devastation at losing a "generous, loving lady".
Mrs Masson's daughter and son-in-law Margaret Langley, 61, and Richard Langley, 63, were injured in the crash, and are in a serious but stable condition in hospital.
In a statement, the couple's children Moe, Carol, Margaret and Jimmy also paid tribute to the emergency services and Virgin Trains for their help.
Two other people also remain in a serious but stable condition in hospital after the London to Glasgow service derailed at Grayrigg.
Speaking at the scene, Deputy Chief Constable Andy Trotter from the British Transport Police said it was too early to say whether the inquiry would be considering criminal charges.
The points "remained the major focal point of the investigation", he said.
Network Rail said it had found nothing of concern after checking 700 similar points in the wake of Friday's crash.
John Armitt, Network Rail's chief executive, told the BBC that disruption to the line was expected to last for between 10 days and two weeks while the investigation was carried out.
Addressing reports the crash could be linked to maintenance issues, he said: "I've no doubt that the people we are employing are qualified and competent to carry out the particular tests we require them to do."
British Transport Police: National police force for railways, also covers London Underground and Midland Metro Tram System
Rail Accident and Investigation Branch: Investigates incidents on railways to improve safety - does not establish blame.
Her Majesty's Railway Inspectorate: Division of the Office of the Rail Regulator, oversees safety on Britain's railways and tramways
He said the additional checks were a precautionary measure that any responsible organisation would undertake.
Transport Secretary Douglas Alexander is expected to make a statement on the crash in the Commons at about 1615 GMT.
Work on removing the train carriages from the site is not expected to begin until the end of the week.
Contractors are currently building two temporary roads from steel across muddy fields to allow heavy lifting gear access, and cranes will take about 48 hours to set up.
"We have been doing a finger-tip search of the site, trying to work around the carriages which, although stable at the moment, we are mindful of the fact that it's a very unstable environment," said Ch Supt Martyn Ripley, of the British Transport Police.
Contractors are working to remove the carriages
Thomas Edwards, who is leading the inquiry for the Rail Accident Investigation Branch (RAIB), said two black box data recorders had been recovered from the wreckage and information from them would now be analysed.
He said, as well as looking at the points, investigators would also be examining the track between the points and where the train slipped down the embankment, signal boxes and the train itself.
A forensic examination carried out by the British Transport Police, the RAIB and Her Majesty's Railway Inspectorate is expected to continue at the site for several days.
Meanwhile there have been calls for an independent public inquiry into the crash.
Louise Christian, the solicitor who represented victims of the 2002 Potters Bar crash, in which seven people died when a train derailed following a points failure, said not enough had been done since then to improve rail safety.
Cumbria Police helpline: 0800 056 0146
Police family liaison centre: 0800 40 50 40
National Rail Enquiries: 08457 48 49 50
Former Transport Secretary Alistair Darling ruled out a public inquiry into Potters Bar but Network Rail and the line maintenance company Jarvis later admitted civil liability in relation to the crash.
Iain Black, 46, the train driver, who suffered a broken collar bone and a broken bone in his neck, is said to be in a serious but stable condition.
Another patient is undergoing neurosurgery.
While the crash investigation continues, buses are being laid on from Lancaster, Preston and Carlisle to replace suspended rail services.