The train and tunnel wall were badly damaged at Camden Town

They hope the meeting at the Commonwealth Institute in west London will head off threatened industrial action over safety fears raised by the unions.

It follows two derailments at Hammersmith on 17 October and Camden Town two days later in which seven people were taken to hospital.

A section of the Northern Line is still shut more than a week after the incident at Camden, causing disruption for thousands of commuters.

When the meeting opened on Tuesday, London's Transport Commissioner Bob Kiley said all sides need to pull together.

We have to do something real that demonstrates that we are serious about this and we have the chance to revive the confidence of our people Tim O'Toole, LU

"This is a call to close ranks, all of us, including the infrastructure companies and the union leadership and to focus on the job at hand," he said.

"Safety is sovereign and that can never take second place to anything else. I do not think there is any person in that room who would disagree with that."

The Rail, Maritime and Transport (RMT) union opposed the privatisation of Tube maintenance on safety grounds and wants it to be returned to London Underground (LU).

LU's managing director Tim O'Toole admitted managers' credibility was at stake following the derailments.

Shutting Camden Town station has hit commuters and stall holders

"I think that the integrity of the enterprise is in balance," said Mr O'Toole.

"We have to do something real that demonstrates that we are serious about this and we have the chance to revive the confidence of our people."

A spokesman for Tube Lines, the private consortium in charge of maintaining the Northern Line, said a report into the Camden crash showed maintenance work met required technical and safety standards.

He said: "The Camden Town area is, unfortunately, a striking example of the immense difficulties we face in renewing and modernising the Tube after decades of under-investment and historically poor decision-making."

The company said it inherited 12,500 'non-compliance notices' about work that had not been done to required standards and was in the process of putting them right.

It added that 260 maintenance people were trying to repair damage to equipment at Camden Town so the station could re-open.

Ballot papers are due to go out this week to RMT members over possible strikes and "go slows" in the run-up to Christmas.

Bob Crow, general secretary of the union, said: "The people doing the work do not feel that London Underground is as safe as it should be.

"We heard nothing today to stop our strike ballot continuing."