At least 85 people have been killed and more than 200 injured in the country's worst peacetime rail crash. The accident happened at 0820 GMT at Harrow, a north-west suburb of London.
A London-bound express train from Perth ploughed into the back of the 0731 Tring-Euston commuter train as it was about to leave Harrow and Wealdstone station, on the London Midland region line.
Seconds later, a third train coming from Euston crashed into the wreckage.
Survivors described hearing a deafening sound like an explosion and then broken glass and debris flying everywhere.