London Underground bosses have called an emergency summit amid concerns over tube safety.

Those attending Tuesday's meeting include managers of the Tubelines and Metronet private maintenance firms and trade union officials, after two derailments on the network within a 36-hour period.

Members of the RMT trade union are being balloted for industrial action over the situation, which could include one-day strikes, go-slows or station closures.

General secretary Bob Crow has called for contracts drawn up under the Public Private Partnership scheme to be withdrawn.

His comments came after it emerged that concerns had been raised over both the Piccadilly line at Hammersmith and the Northern line at Camden Town shortly before the incidents earlier this month.

London Underground managing director Tim O'Toole conceded the reputation of senior staff was on the line.

"I feel that the credibility of this management is at stake," he said.

"I think that the integrity of the enterprise is in balance. 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."

The closed meeting would not be a "talking shop" he insisted.

Speaking outside the meeting, London Transport commissioner Bob Kiley claimed that results from the meeting could emerge "within a matter of days or weeks".

"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.

"This is not going to take forever. The meeting was called quickly and the results will be disseminated quickly. It is an emergency meeting."

Kiley described the move as a "wake-up call", and a chance to address issues arising from current procedures.

"If we or the infrastructure companies are doing things that are inappropriate then that will have to be looked at," he said.

"A broken rail in the Hammersmith incident and a points problem in the Northern line incident - that called into question as to whether maintenance was right."

The Tubelines consortium has released a statement, defending the maintenance work it completed on the Camden Town track.

"The Camden Town area is, unfortunately, a striking example of the immense difficulties we face in renewing and modernising the Tube after decades of underinvestment and historically poor decision-making," it read.

"The delay in restoring service to the Northern line is, in part, because the incident did a lot of damage to the signalling cabling. We have been working round the clock to put all that right.

"It is also because, in carrying out this work, we have found that much of the signalling system does not correspond to the original plans or technical specifications.

"This is just one of countless legacies of the culture of patching up and making do that has characterised the underground for too many years."