Finance is the best path to development Thirteen years ago I chaired the government's Urban Task Force, which was asked to advise on how to build 4m dwellings in England to tackle its long-standing housing shortage. One of our recommendations was that previously developed "brownfield" land could accommodate the vast majority of new housing needed. That, we argued, would allow us to protect the countryside, build homes in a more sustainable way and strengthen and revitalise existing towns and cities, rather than allowing them to spill into sprawl. Sprawl fails us on every count. The soulless tracts of bland development cannot maintain the vitality and intensity of use needed to support transport infrastructure, local shops or community cohesion. It drains the lifeblood from city centres and undermines energy efficient lifestyles. Changing the way we build takes time. Yet the taskforce report has had a significant impact on urban planning . Fifteen years ago, we built 50 per cent of our housing on brownfield sites; today the figure is 75 per cent across England, almost 100 per cent in London. But we still face a chronic shortage of housing, made acute in the past four years as supply has slowed. In the search for scapegoats, the town and country planning system is never far away. Shouldn't we loosen controls, get planners off the backs of householders and developers, even rethink the designation of greenbelt land that has encircled our towns and cities for half a century? But these eagerly-promoted solutions do not address the reality of the problem. In England, there are 330,000 planning permissions for dwellings that have yet to be built. If planning was obstructing delivery we would see a rush to implement these permissions and to secure new ones. The problems are financial. From institutional investors, to grants for social housing, to mortgages for first-time buyers, the funding that fuels construction has dried up. Annual housing completions in England peaked at some 350,000 in the late 1960s, but grew steadily during the last decade to reach 170,000 in 2007-08, before slowing sharply. What happened four years ago was not a sudden shortage of land or an attack of conservatism among planners, but a banking crisis. Our problem is not too much planning; it is not enough investment. In this context, some of the government's recent proposals - debt guarantees for private sector rented housing, new funding for affordable housing, more help for first-time buyers - should make a difference, restoring circulation and unblocking delivery. But the anti-planning subtext to the government's announcement is far more troubling. Delivery delays are compounded by speculative land banking, where housebuilders sit on sites hoping for a capital return - particularly where a change in policy or planning designation is signalled. In these circumstances, "thinking aloud" about the value of green belts is dangerous. Briefings of cabinet discussions and exhortations to local authorities generate uncertainty. If these rumoured proposals took on more concrete form, their effect could be devastating. The incentives to invest in city and town centres - the only environmentally responsible location for new housing - would evaporate; the countryside would begin to be eroded by car-dependent, carbon-intensive, soulless sprawl. Even rumours have consequences. If developers hear subliminal signals and begin to bet on policy change by accumulating land speculatively this will divert scarce capital from investment in urban sites. The result will be a worsening of our current situation, leading to further declines in construction and a widening gap between supply and demand. Just as the housing market starts to recover, it will be kicked back to square one. For 50 years the planning system has, with some success, sought to balance competing interests and claims on land, in one of the most crowded countries in the world. The system is certainly not perfect - as an architect, I have found it phenomenally frustrating at times - but dismantling it is not a serious solution to the profound economic and social challenges that we face. The vitality of nations is founded on the success of cities. Destabilising greenbelt and other planning policy will only suck life out of our urban centres, fetter recovery and worsen the sclerosis in the system rather than do anything to remedy it. The writer is chairman of Rogers Stirk Harbour and Partners