A scaled-down version of the original wave-shaped building, which will be the gateway to the Olympic park in east London, could cost Ј215m.

Culture Secretary Tessa Jowell sent the architect "back to the drawing board" in 2006 because of spiralling costs.

The venue is now due for completion in 2011, two years later than planned.

The wave-shaped roof will now be 14,000 square feet, which is just over a third of the original 35,000 square feet.

Bob Neill, the Conservative Party's London Assembly Olympics spokesman said the original bid of Ј75m was "woefully inadequate".

He said: "You can't have much confidence in a system where something is sent back to save costs and ends up tripling it.

"Two years late and massively over budget and of course a far cry from the original design.

"It's a terrible shame for all those who would have used it to train, all those Londoners who were looking forward to swimming there and of course a big disappointment for all of us who are going to pay for it."

Cost agreed

Olympic chiefs said the cost of the venue has been agreed with the government and would not impact the overall Ј9.3bn budget for London 2012.

However, the final cost of the building would not be released until negotiations with the builders are complete, they said.

Two of the three companies in the running to build the 20,000-seat arena withdrew from the tendering process in November.

After Eiffel and Hochtief decided against making a bid, Balfour Beatty was the only contender.