The eight-carriage Piccadilly Line train, travelling at up to 40 mph, went through Caledonian Road station, north London, with no one in the control cab. It was finally halted 100 yards short of Holloway station by an automatic red signal. When a signal is red a safety device on the track automatically triggers the braking system of any train passing over it.
The train had moved off after the driver alighted at King's Cross to investigate a defective door.
Police and London Underground staff commandeered the next train, emptied it of passengers and set off in pursuit. After pulling up behind the 'runaway', they boarded the empty cab and drove it to Holloway Road station where passengers were interviewed by police.
'It is believed the train moved off through a combination of technical and human error,' a London Underground spokesman said. He insisted there was 'no risk to our customers' and the safety system had worked as it should.
The spokesman said that the east-bound train had developed the defective door at King's Cross at 8.50am. The train moved off while the driver was on the platform.
The train has been taken to the depot at Cockfosters, north London, to be examined. The driver was interviewed and breathalysed, as a matter of course. It was later announced that the test proved negative.
The spokesman said that when a driver left a train he had to do certain things to make it secure. 'We have to find out through our interview with him how he secured the train.' He stressed that there had been no danger to passengers while the train was driverless. 'The train could not have gone into the back of anything else. It was stopped by the first red signal it came to.'Reuse content