London commuters could face further Tube chaos after rail unions rejected London Underground's latest pay offer.

The biggest rail union, the RMT, said the offer was "not enough" and that its executive would be meeting to work out details of a strike ballot.

The train drivers' union Aslef is also due to meet to consider industrial action.

An RMT one-day strike last month caused an almost total shutdown of the Tube and misery for thousands of people trying to get to work.

'Substantial rise'

An RMT spokesman said: "LU has refused point blank to go to mediation.

"They are afraid that mediators would a recommend bigger offer.

"This offer is not enough.

"We are looking for a substantial rise and we also want to sort out other outstanding issues in relation to working conditions."

Bob Mason, London Underground's human resources director, said: "We have urged the unions to reconsider their position and we remain willing to work with them to settle this dispute and to discuss other potential means of improving terms and conditions for their members."