Attempts to unify the city under one leader are doomed because of the disparate nature of the place, says David Walker
This week the Government is publishing a Green Paper on the future shape of the capital's government. It will be incomplete if it takes for granted the existence of "London". No such place exists, for political purposes. Central government has tried to create such an entity before, and the reasons for its failure need to be carefully studied before the same mistake is made again.

The next time you hear someone rattling on about London's government or bemoaning the deficit in representative democracy in the capital, ask yourself this: when they talk about an elected mayor, do they mean a mayor for Heston and for Child's Hill and for Brockley Park (that's the one in Lewisham, not the one in Harrow)? Richard Branson and his ilk may look fine in the West End and at Westminster, but are they seriously intending also to represent Thornton Heath, Whetstone, Gidea Park, Silvertown and East Sheen? It's not that those places are unglamorous or poor, it's that they have no necessary connections with one another or with some amorphous urban entity called London.

Put that another way: London does not exist, in the specific sense of a political region with common interests and the capacity of mobilising a single will that, for example, would approve raising taxes in one area to spend them disproportionately in another - a test of "community" if ever there was one. It's hard enough to do this inside the 32 boroughs, even though most of them are firmly based on historic communities. But the boundary of London - meaning the contiguous urban area - is an accident. If the pre-war Chamberlain government had not enacted green belt legislation when it did, "London" could easily include Bushey (Herts), Thurrock and Redhill.

When London government was reformed in 1963 they reached for the idea of "Greater" London, but it was not then, nor is today, any such thing. Most Londoners have always worked locally. Increasingly, in the outer suburbs people travel outwards, for example to the burgeoning services centre in Croydon or the factory and service depots around the North Circular or Heathrow. Most people don't get on tubes or trains to travel "in".

There is a virtual London, the one to which that Johnsonian cliche about never getting bored may apply, but it is bounded by the Strand, Bayswater and Chelsea. Urban adventurers may try to add new bits, such as Hoxton or Tufnell Park, but this London still has little or nothing to do with the great periphery - Palmers Green, Plumstead, Penge, Pinner. This is the London conjured up weekly by Time Out, a place pulsing with leisure opportunity where, in theory, people can travel across the conurbation for pubs, clubs and football. Only the young middle classes do.

London's divisions go deeper than the inevitable urban pluralism that pits suburbs against poor cores. New York, Paris, Berlin are all divided cities, yet all have possessed political identities for centuries - residents of Queens want Mayor Guiliani to do things in the South Bronx. The residents of Kidbrooke (south east) and Osidge (north) are both in line of sight of the Canary Wharf tower, but do they inhabit the same place, meaning a moral entity where they are prepared to care for their neighbours?

This is no academic question. The reason why Mrs Thatcher was able to do for the Greater London Council was twofold. One was that, despite Ken Livingstone's vast spending of public money, it just was not loved enough. Let's not forget that, until preparations for the 1981 election got under way, one of the strongest advocates for breaking the thing up was ... Ken Livingstone.

The other reason was that Bromley, with the full backing of its people, brought suit against County Hall in the "fares fair" case and won. Have the residents of Bromley suddenly found religion, such that they will now gladly pay up to help house Bermondsey or improve travel prospects for Bethnal Green? Without such a pan-London tax commitment, any mayor and revamped London council will lack legitimacy. Analogies with Scotland break down at every point: Scots know who they are, from Melrose to Milgavie.

A referendum is proposed on the mayoralty. Personalising local government is a wonderful idea but it will only work if we get the place right. A mayor for LCC, Inner London Education Authority, London, maybe. The first question ought to be this: do you belong to London? Let's see what they say in Havering, Hillingdon and Harrow.