Wednesday, October 6, 1999 Published at 12:36 GMT 13:36 UK
Train 'went through red signal'
The trains approach each other on separate tracks
The driver of one of the trains involved in the west London train crash drove through a red signal.
BBC Transport Correspondent Simon Montague says the Thames train also went through two yellow signals before crossing into the path of the oncoming Great Western express.
The Great Western train, which was travelling from Cheltenham to London Paddington, had been given a green light and was proceeding normally.
The red signal in question, known as SN109, has been known to give trouble before. It is an unusual shape, with the red light offset to one side because of visibility problems caused by overhead wiring and pylons.
Mick Ricks, the general secretary of the train drivers' union, Aslef, told BBC News that the problems with this signal had been raised with the appropriate authorities.
He said the drivers wanted the signal to be resited to make it more visible.
Mr Ricks said there had been an incident four years ago and the resulting inquiry had recommended moving the signal. So far, the powers that be had continued to drag their feet on the issue, he said.
Aslef has given the train operators seven days to meet to discuss safety or face ballots on national strike action.