The unpublicised signal failure - revealed in documents leaked to the Independent on Sunday - took place at Auchengray, near Carstairs in Scotland, on a stretch of line used by expresses heading south from Edinburgh at nearly 100mph.
The new commercial culture of the track and signalling company was a contributory cause, according to a memo from a senior Railtrack official, Roy Bell, to his boss.
A collision would have been inevitable if a signalman had not spotted the failure. A four-mile section of track was left unprotected because a signal did not stay on red after a train passed, but changed back to green. The section of track had been the subject of repair work over the weekend and had been handed back on 20 May, when the incident occurred.
Mr Bell, a signalling expert who was the main BR witness at the inquiry into the Clapham disaster, wrote that the incident was a "very serious wrong-side [a potentially dangerous] failure".
His memo says that the preliminary investigation uncovered eight errors, including faulty design, inadequate documentation, faulty testing procedures and "inadequate use of the test train".
The memo says: "The only reason that the Auchingray incident was discovered so soon was the lucky chance that the signalman at Motherwell Signalling Centre had an indication of MC424 [the signal] on his panel and by vigilance noticed its incorrect operation."
Mr Bell, who according to Railtrack is on sick leave, said in his memo: "If we are to safely progress into the future, we must hold an in-depth inquiry, led by Railtrack HQ, to probe very deeply into the management and organisational issues which need to be urgently addressed.
"What concerns me much more than the actual deficiencies by front-line staff is the fact that many of them were people I have known previously to be very competent and conscientious. Why then have their standards slipped?"
He points out that the inquiry into the Clapham disaster recommended that "BR shall ensure that the organisational framework exists to prevent commercial considerations of a business-led railway from compromising safety."
A former senior rail manager commented: "At Clapham, there was half a mile of track left unprotected [by a signal] and the speed limit was 40 to 60mph. Here the trains can go up to 95mph and there were four-and-a- half miles left unprotected."
A spokeswoman for Railtrack said: "There was no danger to the public. This was an empty train that was being used to test the equipment and the fault was found straightaway."
Last year, however, Railtrack was forced to apologise after a similar incident led to several trains going through signals. The company initially said the failures had occurred "during testing". It later transpired that passenger trains were on the track.
Glenda Jackson, Labour's transport spokewoman, demanded a full inquiry.Reuse content