Fears over Tube safety after two trains derail in 48 hours

Fears over safety on London Underground trains mounted yesterday when a second train derailed in 48 hours, injuring seven people and causing massive disruption for thousands of passengers.

The accident, which will also rekindle controversy over a Tube privatisation scheme, happened when the end carriage of a Northern line train left the track and smashed into the wall of a tunnel as it approached Camden Town.

Safety experts warned of possible further, and more serious, accidents unless the faults causing the derailment were quickly discovered. And the country's biggest rail unions threatened to take industrial action unless the private contracts for track maintenance were suspended.

The unions claimed that drivers had recently, and repeatedly, warned about problems on the track in north London. Maintenance work on points had been carried out on that stretch on Saturday night. London Underground said early indications were that the derailment was due to faults on the track rather than the train.

An investigation by Transport for London will consider whether the work, carried out by the private firm Tube Lines, which includes Jarvis among its shareholders, had played any part in the accident. Jarvis is at the centre of the continuing investigation into the Potters Bar rail crash in May 2002, in which seven people died.

Five men and two women were taken to the Royal Free Hospital in Hampstead after the accident just after 10am yesterday. A man in his late 30s broke his thigh and a man in his 20s suffered a head injury. Seven others were treated at the scene for minor injuries. All the injured were in the last of the train's six carriages which became detached from the others 30 metres inside the tunnel.

On Friday a Piccadilly Line train came off the track between Hammersmith and Barons Court stations in west London.

Bob Crow, general secretary of the RMT Union, said : "If the Mayor of London, Transport Commissioner or the Government do not take action to suspend these contracts, then I shall be recommending to my executives and to the other rail unions on London Underground that we ballot to take strike action to defend the safety of our members and the travelling public." Aslef, the train drivers' union, also said it had "serious concerns" about the maintenance regime.

The Mayor, Ken Livingstone, who vigorously opposed the public-private partnership for the Tube, said the derailments raised "grave" safety doubts.