Ken Livingstone has renewed his call for unions and Tube bosses to avoid next week's strike.

The London mayor revealed on Friday he has asked an employment arbitration expert to step in to resolve the row between London Underground and the RMT union.

Eight employees of Metronet, the private firm which runs part of the network, were dismissed after empty beer cans were found in a station room.

"There is not a shred of evidence that says any of these men were guilty," said RMT general secretary Bob Crow.

But Livingstone has described the strike as "absolutely bizarre" and sought to claim the middle ground.

Though drinking at work could not be condoned, he argued, "there has to be a burden of proof".

He revealed he has written to Raj Singh, regional chairman of the Employment Tribunal, asking for him to examine the case.

"Every Londoner wants to see the dispute between Metronet and the RMT resolved," said Livingstone.

"In the meantime, I would also urge both parties to respond to the offer of assistance by ACAS in finding a negotiated solution."