An interim report by the Health and Safety Executive said the immediate cause of the crash appeared to be a commuter train jumping a red light, but it said the root causes were likely to be complex.

Police now believe at least 40 people were killed when the Thames train ploughed into a packed Great Western commuter train in west London on Tuesday morning.

A further 64 are still unaccounted for, although that figure is expected to fall as people reported missing contact the police.

The HSE said the Thames train passed signal 109 at red outside Paddington Station in London, before colliding with the Great Western just 700 metres further on.

But it says driver error was only one factor in the accident.

The report says the crash could have been avoided if the Train Protection Warning System (TPWS) - which would have automatically stopped the commuter service run by Thames Trains - had been installed on the signal and working properly.

The BBC's Ben Brown:"The authorities have moved with unprecedented speed"

Signal 109, which Railtrack has been ordered to stop using until safety improvements are made, was due to have TPWS fitted by the year 2003.

It has also emerged that the approach to Paddington station had been speeded up on the basis that all trains would be fitted with the high-tech Automatic Train Protection (ATP) system, but this did not happen.

If the system had been fitted to the Thames train, as well as the Great Western, it would have been forced to stop and the disaster may never have happened, former British Rail executive Bob Poynter told Channel 4 news.

Click here to see the site of the crash

Introducing the HSE report, Chief Inspector of Railways Vic Coleman said the crash was not being blamed on the driver.

Flowers have been left at Reading station

He said: "We see this, at present, as a system failure."

The signalling equipment was unlikely to have been at fault, the report says.

It is possible that the brakes failed on the commuter train.

The type of Automatic Warning System fitted to the Thames train, the AWS, should have alerted the driver that he had passed the signals and, if not cancelled, applied the brakes.

However, it was possible the AWS had not been functioning properly.

As well as publishing the report, the HSE also told Railtrack to immediately stop using signal 109, to improve the worst 22 signals in the country, and to modify all signals passed at red more than once.

Bodies were still being removed on Friday

And it wrote to Great Western after it emerged the ATP system had not been switched on, even though this was unlikely to have had a bearing on the accident.

All train operating companies have also been told to give drivers refresher training on danger signals.

Lord MacDonald:"What we need is a culture of safety"

The HSE is to produce a full report. A separate public inquiry will start shortly, headed by Lord Cullen.

The HSE says it will now focus on three main questions - why the crash happened, what action should be taken now to prevent further accidents, and whether any enforcement action, including prosecution, is justified.

There could be prosecutions under the Health and Safety at Work Act if there is evidence of gross neglect, says the HSE.

The Crown Prosecution Service could even be asked to consider a charge of manslaughter.

The grief becomes too much to bear

Thames train driver Michael Hodder, 31, a father-of-two who had formerly served in the Royal Navy, died in the crash. He had only qualified as a driver two months ago.

His brother Graham said: "Until the facts of the incident are properly known, we find it hard to accept the accusations levelled at Michael when no-one, the police, rail companies or press, have any evidence whatsoever."

The BBC's George Eykyn:"At least forty people died"

The driver of the Great Western train also died. He was named on Friday as grandfather-of-two Brian Cooper, 52, from Hayes in west London.

At the crash site, the search for those who died, for identification belonging to the dead, and for evidence, is continuing.

Structural experts worked throughout the day on Friday to secure the wreckage of the Great Western train, especially the most badly-burned carriage, carriage H, in which an unknown number died.

The emergency police number is 0171 834 7777. Worried relatives and friends should call the same number.

All people on the train or witnesses nearby are also asked to call the British Transport Police answerphone on 0800 405040 and leave their name and numbers so they can be contacted as part of the inquiry.

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