The Department of the Environment demolishes its headquarters to make way for the car culture

The number of car-parking spaces on a key government site in central London would quadruple to more than 1,000 if the design which yesterday won a major architectural competition is built.

Environmental campaigners were outraged at the notion of multiplying parking space in the heart of congested Westminster borough - especially since the Secretary of State for the Environment, John Gummer, says he is determined the huge new development at Marsham Street will improve the quality of the local environment.

Demolition of the three brutalist and much-hated high-rise towers which now house the Departments of Environment and Transport is due to start next spring. Yesterday Mr Gummer announced that a passionately pro-European Italian architect had won the competition for a masterplan for the two- hectare site, one of the most important in central London.

But Gabriele Tagliaventi's winning entry for offices, shops and homes includes space for 1,200 cars in its basements - compared to the 300 spaces within the existing, 25-year-old building. Yet government planning policies now aim to encourage people to use public transport in city centres.

Roger Higman, transport campaigner with the environmental pressure group Friends of the Earth, said: "Ministers have got to lead from the front. This has be to rethought very, very quickly."

Michael Gwilliam, director of the Civic Trust, said: "While we support the Government's overall concept for that site, the car parking figures in the winning entry need to be rethought. It's a lot of space."

Mr Tagliaventi's design includes a swimming-pool and cinema. There will be a large central square, streets criss-crossing the site (none do at present) and 10 separate blocks up to eight storeys high.

Mr Gummer said the Marsham Street redevelopment was "the first major contribution by a Government in 50 years to the betterment of London. It will change the whole tone of the area".

Mr Tagliaventi's winning design, which earned him pounds 25,000, was picked by a 12-person panel which included the Deputy Prime Minister, Michael Heseltine, Mr Gummer, the modernist architect Will Alsop and the traditionalist Leon Krier, who advises the Prince of Wales.

The buildings in the designlook classical, as do those in most of the competition's top 10 entries. But Mr Gummer said what had won was the overall design, not the architectural style. There will be a further competition to design the individual buildings and some of the winners may be modernist.

Mr Tagliaventi, 36, said his firm of eight architects from Bologna wanted to specialise in projects which reflected closer European union. "I love this idea," he added.

He had been inspired by the works of the Regency architect and town planner John Nash. His design set out to let people live and work in the same place, to fit in with the surrounding buildings, connect nearby streets "and to look natural, so that people looking at it think it was done in the past".

The Government still has to decide whether it will take any office space in the new development, and whether it will sell the entire site off to a developer or maintain some ownership. The Departments of Transport and Environment, which employ far fewer people than 25 years ago, have already started moving out.

A Department of the Environment spokesman said that the number of car- parking spaces had yet to be decided, but they would conform with Westminster City Council's codes, which were aimed at clamping down on the growth in car-parking spaces in central London.