A decision by Britain's Attorney General Lord Williams that all evidence presented to a public inquiry into the Paddington train disaster in London will be excluded from any future legal action means that rail companies and others suspected of corporate manslaughter could escape prosecution.

The decision makes a mockery of investigations by the British Transport Police into the crash that killed 31 people and injured 250 in October last year. Two trains collided outside Paddington station after one of them passed a partially obscured red danger signal. Initial investigations into the cause of the crash showed that under-investment by Railtrack—the company responsible for signalling and track maintenance—played a significant role.

The company had received complaints from drivers on several occasions that the now infamous Signal 109 was hidden from the view, but had taken no action. It had planned to change the signal the month the crash took place. This was six months after an independent report recommended the siting of low-level signals on the 109 gantry as an extra aid to drivers. It took six meetings from April to October last year for the change to be approved.

The rail industry as a whole was heavily criticised by the Railway Inspectorate even prior to last October's disaster. Incidents of Signal Passed at Danger (SPADs) were up 8 percent in 1998, to 643. In an unpublished report on SPADs, the Inspectorate blamed Railtrack and the train operating companies for the increasing number of incidents. It said remedial action had been inadequate. Railtrack and the two train companies involved in the Paddington crash, Great Western and Thames, were expected to face charges of corporate manslaughter. According to the Guardian newspaper, criminal investigations were also under way into the Health & Safety Executive. But any possible prosecution has been thwarted by the promise of immunity, which means there are likely to be no documents left that could support a case against individuals or the companies.

Superintendent Tony Thompson of the British Transport Police said: "If certain key documents aren't admissible, it tears the heart out of any potential prosecution. A lot of the stuff we will be relying on for a prosecution is going to be looked at by the inquiry. Once it's admitted and subjected to the immunity, there is virtually nothing left to base a case on."

Louise Christian, a solicitor representing eight of the victims' families, accused the government of taking a political decision to block prosecutions. "This means there has been a decision by the government not to prosecute and that is very disturbing. On something as political as the railways and the crash, the decision to prosecute or not should be taken by a wholly independent authority and not the government," she said.