Just as all successful home extensions steer clear of the kitchen, so do all successful development plans steer clear of cities. Once you start tinkering with cities it is the same as tinkering with a domestic plumbing system. Soon you have to turn off the water, re-route the drainage, muck about with the gas and fight with the electricity. Every utility gets involved and - conventional wisdom to the contrary - getting every utility involved is a recipe for ruin, not for home improvements.
Take Berlin, for example: it is a city with an administration admirably organised for learning on its feet and, unlike some cities, one not ashamed to face the facts, even when they stubbornly refuse to conform to its own trumpeted predictions.
Six or seven years ago, in the gleeful aftermath of reunification and the decision to return the capital to Berlin, everyone - from the highest politician in the land to the lowliest property developer - assumed that the result would be an influx of people. The city would regain its pre- war population and go on to match the size of London and Paris. City planners looked to reduce green areas and double the population density of the inner city, as well as accommodating more than a million people in new suburbs. Much building was set in train to accommodate this great expansion, but soon it appeared that the city's prospects for growth had been greatly exaggerated. Today, with more hotel rooms and apartments than it has visitors or would-be residents, Berlin is facing a loss of population. The relevance for London could not be more marked, and we can learn from it.
In calculating their mythical increase in population, German planners had overlooked historical facts, most importantly that in 40 years as West Germany's provisional capital, the population of Bonn had increased by only 100,000 people. In the same way the population of East Berlin, capital of the centrally administered German Democratic Republic, increased by only 8 per cent between 1949 and 1989. Since two-thirds of today's enlarged Germany is still governed as it was under the old, administratively decentralised West German Federal Republic, there is no more structural demand for a concentration of population in Berlin than there was in Bonn. As a result, Berlin's population is now expected to fall as much as 250,000 by 2015, as a result of low internal immigration, the low birth- rate of its present population, and a continuing exodus of young Berliners to the decentralised West. Unless immigration or relocation to Berlin dramatically increases, the city will return to the declining population pattern of the years of the Berlin Wall.
What the Berlin story tells us is that population trends are truly intractable. Not only do they barely respond to the most drastic governmental measures, they tend to revert to their long-term trends whenever they can. Berlin was bombed into the Stone Age in World War II, then was divided for 40 years, during which time most of Germany was decentralised. All of that history was necessary to bring about Berlin's present low population status, which is proving as hard to put into reverse as a supertanker. In short, designating Berlin the capital city has had no effect, and may not for many years.
Notwithstanding its missionary zeal, the efforts of Lord Rogers' Urban Task Force will face the same kind of impasse in London. Though less dramatic than Berlin's history, London's is longer. The 'dis-urbanisation' of England began with the railways in the nineteenth century and has been completed by the private car in the twentieth. The problem of turning back a trend this profound is bigger than anybody thinks.