The train and tunnel wall were badly damaged at Camden Town

It was hoped the meeting with Tube bosses at the Commonwealth Institute in west London would head off threatened strikes 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.

London Underground (LU) told the meeting it hoped the Northern Line between Golders Green and Charing Cross would be open on Wednesday morning.

Employees' support

London Underground Managing Director Tim O'Toole promised to investigate Tube safety.

He said: "Today, we had a frank exchange of views, but it was a constructive discussion. We promised to investigate every individual concern raised by the unions today, and report back to them on the action taken.

"We count on the support of all our employees to keep London Underground safe. Our goal today was to make sure they know that and that we will make changes to improve Underground safety."

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

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.

We heard nothing today to stop our strike ballot continuing Bob Crow, RMT general secretary

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."