A pair of nuts found detached from the points at the centre of the Potters Bar rail crash were discovered loose nine days before the accident, it was revealed today.
The revelation came as engineers began moving the rail carriage that crashed into the station in last Friday's crash, which killed seven and injured 76.
An official interim report published today said safety officials were continuing to look at rail maintenance schedules and practices.
The Health and Safety Executive confirmed that early indications suggested a fault in a set of points south of the station caused the derailment.
The report said track maintenance records, particularly those in relation to the points, had been secured by British Transport Police (BTP).
The BTP also has a video film of the event - believed to have been recorded by station cameras - and this will be examined in detail, said the HSE.
The fourth carriage of a West Anglia Great Northern (WAGN) service from London to King's Lynn was derailed and ended up wedged under the station canopy.
Today's report said there was no evidence so far to support the theory that the points had been vandalised or deliberately damaged. There was also no evidence the signals were at fault or the train was being badly driven.
The report said that the WAGN train was travelling up to 100 mph and that the rear part of the train derailed about 150 metres to the south of the station.
"Evidence suggests that the points in question moved as the rear of the third carriage of the train passed over them, deflecting the fourth and last carriage towards the left.
"It is believed this happened because nuts on two stretcher bars were detached. The locking bar connecting the tips of the points was then subject to forces normally shared by the stretchers, and it failed." the report said.
PA