Despite a second police investigation, prosecutors believe it would be too difficult to prove that Railtrack managers were “grossly negligent”, according to sources close to the case.

The Crown Prosecution Service (CPS) is likely to announce its decision next month to drop criminal proceedings. This would mean that no company or manager will have been convicted of manslaughter for any rail crash in Britain.

The crash at Ladbroke Grove, west London, in October 1999 happened when the driver of a Thames Trains commuter service went through a red signal numbered SN109 outside Paddington station and collided head-on with a Great Western inter-city express.

A public inquiry into the crash, headed by Lord Cullen, found that Railtrack, now Network Rail, had been repeatedly warned about the difficulty of reading signals in the area, including signal SN109.

Two years after the disaster — the worst involving a train since 35 people were killed at Clapham, south London, in 1988 — the CPS advised British transport police to wind down its investigation. In May 2002, following pressure from bereaved relatives, officers were asked to re-open the inquiry, focusing on track management and signal layout at Paddington.

Detectives are thought to have uncovered fresh evidence, but prosecutors believe this would be insufficient to secure a manslaughter conviction. “We are expecting a decision imminently and they (the CPS) are probably going the same way as Potters Bar,” said a source.

The CPS will not bring criminal charges in relation to the crash in Potters Bar, Hertfordshire, in May 2002, in which seven passengers died.

The acquittal this year of rail managers charged with manslaughter over the Hatfield train crash is thought to be pivotal in the CPS’s reluctance to pursue criminal proceedings over Ladbroke Grove. The Hatfield case, following the death of four passengers in October 2000, collapsed after the judge ruled there was insufficient evidence for proving “gross negligence” on the part of an individual.

The Ladbroke Grove inquiry is now likely to be passed to the Health and Safety Executive.

A CPS spokesman said: “No decision has been made yet. The evidence is still under review.”