Liberating London: Should Nelson and Churchill look down on car- free zones?

Why does it require personages of the rank of Deputy Prime Minister and Secretary of State for Culture to launch a public consultation on closing parts of two London squares to traffic?

At a press conference to-morrow morning, John Prescott and Chris Smith, accompanied by one of the world's best architects, Sir Norman Foster, will describe proposals to ban vehicles from the north side of Trafalgar Square, where the National Gallery stands, and likewise to close the south side of Parliament Square, next to Westminster Abbey. They will also outline a second option which would ban all traffic except buses from the east side (dominated by St Martin-in-the-Fields) and take a more generous, pro-pedestrian approach to Whitehall and Parliament Square.

Both plans include smaller proposals for the surrounding streets, to help people move around more easily, ease the path of cyclists and improve the appearance of the area. Trees would be established; the magnificent courtyards of the Treasury and the Foreign Office would be opened to the public; Old Palace Yard, currently a car park for the House of Lords, would become a new square.

Ministers' involvement is appropriate, for this concerns the very heart of the nation, the seat of government, ceremonial routes and, in Trafalgar Square, the place for great open-air meetings and demonstrations.

The Houses of Parliament and Westminster Abbey are together classified as a World Heritage Site, on a par with the Pyramids and the Taj Mahal. The initiative is of historic importance, too, because for the first time the Government is enlisted in the task of restraining the motor car in city centres. It is just about 100 years since cars first began to traverse the north side of Trafalgar Square and terrify pedestrians wishing to cross to the paved centre, with Nelson's Column and the pigeons.

The genesis of the two plans was a huge public meeting organised by the Architecture Foundation and the Evening Standard in April last year, at which Tony Blair spoke, and where Sir Norman floated the notion that the time had come to start removing cars from the centre of London. A few weeks later, three Conservative ministers, John Gummer, Virginia Bottomley and Sir George Young, decided to stage a competition to select a team for studying the area with a view to producing proposals - which Sir Norman duly won. The transition between the previous government and the present one has been seamless. It has become a bipartisan policy.

But Sir Norman and his architectural practice did not win on their own. Sir Norman leads a consortium containing Halcrow Fox, road traffic consultants, and Space Syntax Laboratory, which studies the way people move around cities. Readers walking along Whitehall from Trafalgar Square to Westminster Abbey this summer who thought they were being followed, probably were.

It may seem obvious that architect, traffic planner and pedestrian analyst should work together, but until now it has rarely been undertaken. While Space Syntax was watching where people walk, Halcrow Fox was plotting the consequences for private traffic. The upshot would not be gridlocked streets in the centre; rather, the effects would ripple outwards over a wide area of London, from Kings Cross in the North to the south bank of the Thames, producing heavier traffic flows at a variety of points. The average increase in journey times is calculated at half to one minute.

No buildings will be pulled down, no new structures erected, no roads diverted. All the proposed interventions are small scale.

In one important respect, the London proposals exceed what is being done, for example, in Berlin or Barcelona, and that it is in the amount of consultation. Berlin is being rebuilt as it was in the 19th century, without the public having much of a say. The same goes for Barcelona, where a strong mayor has had his way - albeit to good effect.

This is not the London method. Already 130 organisations and statutory bodies have been consulted. While Westminster Abbey, for instance, would welcome the removal of traffic from directly outside its walls, the Queen Elizabeth Conference Centre on the other side of the square has expressed concern about access for the thousands of people who attend meetings there. Now the general public is also to be consulted.

Whether to approve, turns on a number of issues. Do we want to find a new balance between the car on the one hand, and pedestrians and public transport on the other? If we do move against the car, are we willing to accept the increased congestion, and higher costs for business, in surrounding areas? Or do we believe that making the inner city more attractive would bring in more visitors and thus yield counter-balancing economic gains?

So important are questions like these that the nearer the politicians have got to the period for public consultation, the clearer they seem to have become about the primacy of people's desires. That is why they are launching the initiative themselves. Moreover, without public support, nothing will go forward.