Plans to transform Parliament Square into a pedestrianised piazza in time for the Olympics have been shelved by Boris Johnson.
The Mayor's office said he was reviewing the proposals amid concern that closing off streets would cause jams.
But sources close to the £18 million project, originally given the go-ahead by Ken Livingstone, claimed it had been abandoned to avoid angering motorists.
One said: "We've got a Tory Mayor and Parliament Square is in a Tory borough. Neither wants to lose votes because of stopping people driving across London."
Under the plans, the road in front of Westminster Abbey would be closed to cars and the lawn at the centre replaced with stone paving and benches. The new design was predicted to attract 30 million visitors a year.
Mr Johnson suggested to Building Design magazine that Parliament Square was unlikely to be the only major public space scheme to go back to the drawing board or be scrapped.
"The butterflies and the trees and architects' plans - I love all that and I think that people will, you know, generally like them very much," he said.
"There are some differences about some of the proposals currently on the drawing board and I don't want to get dragged into a discussion - because a lot of them are under review now. But I'm strongly attracted personally to things which give people a sense of ownership over public space, particularly cyclists."
The redesign was abandoned by Transport for London after studies found it would worsen congestion. A spokesman for Mr Johnson said: "The Mayor has requested further work to be carried out on the Parliament Square Improvement project before giving the go-ahead for the next stages.
This follows concerns with the possible traffic impact, which are supported by Transport for London's advice."
But Green London Assembly member Jenny Jones criticised the Mayor for shelving the project.
"Boris seems incapable of making the tough decisions needed to improve London's environment," she said. "There were huge complaints from motorists ahead of the redesign of Trafalgar Square, but the previous Mayor faced them down. Trafalgar Square was transformed from a famous monument on a traffic island into a well used and loved public space. If Boris hasn't got the guts to make tough decisions, then all his talk of a beautiful London filled with trees, birds and clean air is meaningless."
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The Parliament Square plan was part of a Design for London scheme to create or upgrade 100 public spaces, including Brixton central square, Exhibition Road and Euston Circus.
Daniel Moylan, chairman of London Councils' transport and environment committee, said: "The Mayor has a fantastic opportunity to make London's streets better in time for the Olympics. We'll be very embarrassed if he does not do that in front of millions of visitors."
