London Tory mayoral contender Steve Norris has come under fire after it was announced he is to become chairman of the Jarvis construction firm.

Norris will replace executive chairman Paris Moayedi, who announced his resignation on Tuesday, on an interim basis.

The company came under fire for alleged maintenance failures and was involved in repairing the track on which the Potters Bar rail crash occurred.

The former transport minister said he would still fight to become London's mayor and vowed to step down from Jarvis if elected.

"I have made it very clear that I am still dedicated to the London mayoral elections in June 2004 where I am the Conservative candidate, but I will help Jarvis through the present situation and get the right person in place to succeed," he said.

Ken Livingstone said Norris had firmly pinned his colours to the privatisation mast.

"Londoners will now have a straight choice between me and Steve Norris about how to deliver public services - one for the travelling public, one for the privatised companies responsible for track and signals on the Tube," he said.

"But at least Mr Norris, unlike Simon Hughes, has today made it clear that he would be a full-time mayor if he was elected.

Hughes, the Liberal Democrats' candidate, accused Norris of a conflict of interest.

"It will prevent Mr Norris making any objective comments on any Tube issues from now on, despite this being one of the key responsibilities of the London mayor.

"I hope, at even this late stage, Mr Norris will accept that this is a direct clash of interest, not just in theory but in practice."

Labour's official candidate Nicky Gavron expressed anger at Norris's appointment.

"I am astounded that Steve Norris should consider such a conflict of interest. He has either completely lost the plot or is not serious about running for mayor. Voters need someone who will stand up for London rather than put shareholder interests first," she said.

"This just goes to show that the Tories have learnt nothing from their past mistakes.

"Steve Norris is obviously more concerned about his own business interests than representing the needs of the travelling public."

But a spokesman for the Conservative candidate's campaign defended the move.

"The fact Steve Norris has been asked to sort out Jarvis shows he is a serious business figure, unlike the other candidates," he said.

"What the capital needs is someone who can tackle the problems that matter most to Londoner's like crime and transport.

"Steve's number one priority is winning the mayoralty of London."