LONDON Underground was at a standstill today as thousands of workers "solidly" supported a strike, causing travel chaos across the capital.

Commuters packed on to buses or walked to work in bright sunshine, with Tube services set to be disrupted until tomorrow morning.

Business groups said the strike will cost the capital's economy tens of millions of pounds. The Government and London mayor Boris Johnson condemned the action but unions said LU was to blame.

Picket lines were mounted outside Tube stations by members of four trade unions involved in the action in a row over the new all-night Tubes, due to start in mid-September.

LU's boss warned that the strike will cause "big disruption" and branded it "totally unnecessary". Managing director Mike Brown said in a message to passengers that the company had "strained every muscle" to put together a "remarkably fair" pay offer for the introduction of the new Tubes.

"I am very sorry your journey has been disrupted. This strike is unnecessary," he said.

"The numbers using London Underground late at night have almost doubled over the last decade, and because of recent sustained investment in modernising your Tube network we can run overnight on Fridays and Saturdays on five lines from later this year."

Steve Griffiths, LU chief operating officer, said: "A night-time Tube service is something Londoners and businesses have been requesting for many years. It will make life easier for everyone, cut journey times, create jobs and boost the economy.

"We want to reward our staff for its delivery and have been open and transparent in our negotiations with the trade unions - but unfortunately they have failed to engage.

"We have put forward a very, very fair offer, which consists of an average salary increase of 2%, 1% or RPI (whichever is greater) for next year and the one after, plus a £500 night Tube launch bonus and an additional £2,000 bonus for night Tube train drivers.

"No one will have to work more hours than they do now, and we have a longer term plan, which will mean no one will need to work nights if they don't want to."

RMT general secretary Mick Cash said: "The strike action on London Underground is rock solid across all lines and depots and the unity and solidarity of the entire workforce, which has now brought London to a standstill, must force the Tube bosses back to the negotiating table to address the issues at the heart of this dispute.

"That means an end to the attempt to bulldoze through new working patterns that would wreck work/life balance and leave staff in safety critical jobs burnt out and stressed out at a time when Tube services are facing unprecedented demand.

"We've wasted three months in negotiations that failed to address staff concerns and it's essential for London that there's no repeat and that puts the ball firmly in LU's court."

TSSA leader Manuel Cortes called for peace talks to start at Acas tomorrow.

He said: "No one wants to see London at a standstill, least of all our members, so it is high time for LU to come back to the negotiating table.

"They should stop playing games and start talking to us in good faith to get a sensible solution to this dispute.

"We are ready and willing to be at Acas tomorrow morning to sort this out. It is time to end the blame game and agree a solution which keeps London moving and secures the start of the night Tube in September."

London Mayor Boris Johnson said the strike was "totally unnecessary" and was causing huge disruption to Londoners and to businesses.

"I think most reasonable people will look at the offer that's on the table from London Underground and find it impossible to fathom why the unions are rejecting it," he said.

"I also think it's extraordinary that the union leadership hasn't even put the offer back to their members to formally consider.

"We are going to get on with the night Tube and ultimately this strike will achieve nothing. Londoners will no doubt show resolve and resourcefulness in getting to where they need to go."

LU said it had received no response to the latest "fair and competitive" pay offer made to unions on Monday, urging that it be put to workers.