ARCHITECTURE / An English drama: The look of central London is threatened by a new law. Peter York explains

EATON SQUARE SW1, the spiritual centre of the Grosvenor Estate, where a short lease on a two-bedroom flat can cost pounds 1.25m, is nice to film in. It's what people describe as 'very English' - a euphemism for posh - and is actually rather film-settish. Uniform cream stucco facades, black doors and ironwork, lots of service extras quietly busying around - chauffeurs, Filipino helps, plumbers who look as if they've done apprenticeships. It all creates an impression of unnatural, un-English order, as if - you can't help thinking - the place was privately policed.

And film stars live there too. While filming Eaton Square for a BBC2 programme on London's Great Estates, we heard that both Roger Moore and Sean Connery had flats in the short stretch we'd covered. And there were other famous people all around; you could have started a Hollywood tour.

The names have it in the smartest parts of London. Trace the names and you find a live grandee: Grosvenor Square (Gerald Grosvenor, Duke of Westminster), Cadogan Square (the Earl of Cadogan), Portman Square (Viscount Portman). Trace the names of the sidestreets and you find someone who married into the family in 1790, a transaction commemorated.

The Great Estates - The Crown (Regent's Park, Kensington), Grosvenor (Mayfair, Belgravia), Cadogan (Chelsea), De Walden ('doctor-land' between Hallam Street and Marylebone High Street), Portman (Marble Arch to Marylebone Road) and a group of smaller, aristocratic land- owners with valuable 'packages' such as Viscount Petersham, grandfather- in-law of Viscount Linley, who has a chunk of stucco South Kensington - still own between them several thousand acres of prime central London.

Yolanda Barnes, head of research for Savills, the property consultants, estimates that in central London, at least 60 per cent of prime residential is on the Great Estates.

According to the experts, the 'value factors' that maintain prices on the Great Estates are lots of period property (everyone except Arabs and Far Easterners claims to prefer it now) with a cohesive look - ie unbroken squares and terraces with the same paintwork livery - which is well-maintained. The good stuff is listed Old London Theme Park and the cleverest estates, like the Grosvenor, go to Disney-like trouble to maintain control. It's been worth their while because it's guaranteed the highest rentals, the best leasehold prices and the biggest developers wanting to work with them.

The landlords, good and indifferent, account for the look of the central London tourists see and rich people live in. The issue of looks is the key to the tourist trade, and to the battle for eventual Euro-capital between London, Haussmann's Paris and Berlin (the best architecture of East Berlin is being restored at a lick).

The grand residential areas of the big European capitals are essentially international now. Every developer, every social engineer, recognises that to sell a city you need agreeable domestic places that attract the investors' wives. The big landlords are important because they guarantee a London fit for rich people to live in; because they've got a huge interest in being good conservationists. So long as they own their freeholds, that is.

The Leasehold Reform, Housing and Urban Development Act of 1993 threatens that interest because it gives leaseholders the right to buy their freeholds. And the largest collections of relevant leaseholds are on the Great Estates in London. If everyone exercised their right over the next, say, 20 years, the distinctive look of the great estates could go. If the nobs own less than, say, 50 per cent of a particular terrace or square, they won't have the right or incentive to police it, to stop the PVC windows at No 5 and the illegal Balkan travel agency knocking about the listed plasterwork at No 12. The local authorities and English Heritage can't do it, say the grandees' managers, they haven't got the manpower, the local knowledge or the incentive. The statutory powers aren't enough when you're dealing with thousands of flats and houses. You've got to have clout. You've got to have the long view. The very long view. The family view.

Publicly the grandees have wrapped themselves in the conservation flag. After us, the deluge. Central London will be a Bladerunner hell, another Moscow. Stuart Corbyn, chief executive of the Cadogan Estates, says: 'Without the estate to keep up standards, some buildings may start to get run down, people will open offices in them, or anything really, even small brothels.' Privately they mutter about the New Tories who saw the Act through being in it for the money; helping their rich friends make a fast buck. The predictable irony is that the richer the leaseholder the more likely he is to benefit. He'll have the money for the solicitor's bills and the freehold. It won't be cheap and he'll stand to make the most.

The Act was designed to let people in flats get out of the control of bad landlords, though no freeholds have been bought yet on the Great Estates. It's a difficult process. There have to be at least three flats in your block, and at least two-thirds of the residents have to want to buy. Then there's the cost, because you must also compensate the freeholder for the effect on the rest of their holdings of your purchase. If the parties can't agree, they go to a Leasehold Valuation Tribunal. As for foreigners, an amendment agreed by the Lords requires the flat to be your primary residence. So if more than a third of the people in your block don't live primarily in England you don't qualify.

We're in the phoney-war period now. Leaseholders are starting to consider their rights, enterprising lawyers are touting their services, clever property men are working out how they can buy tranches of grandee London by stealth - and nothing has changed.

While it's still bubbling under we need to be clear what we want for London, and what effect leasehold reform will have. We need to evaluate the grandees' claims - are they really such good stewards? Simon Jenkins, the journalist and author of Landlords to London, is sceptical. He believes they have always gone for profit. He cites, among others, the Portman Estate demolishing fine Grade One houses for the redevelopment of Baker Street.

English Heritage has a plan to maintain values in a period of transition. Under the Act, they have the power to impose Estate Management Schemes similar to the Great Estates' policing controls. So if you buy your freehold on a Great Estate, you'll probably still be bound by the restrictions in your lease. But can they really make it work everywhere in historic London?

It's a wonderful English drama. It has class tensions, setting grandees against Thatcherite Tories - Westminster resigned from the party over this, and Cadogan withdrew financial support. It has individual rights and aspirations - every Englishman a freeholder - against the collective of architectural history.

As we interviewed nobs and experts, and panned the camera around uniform porticoes in SW1 and louche multicoloured terraces in W11, I became less certain about the rights involved, about the motives and the likely outcomes, and more convinced it all deserved airing and debate. Forget the Tower of London ravens; when Sean and Roger leave Eaton Square for first-floor fronts behind Berlin gingerbread, we'll have a problem.