People don't understand what a brownfield site is - they think it's a piece of land covered in 45-gallon drums leaking chemicals,' says Scott-Wilson director Peter Guthrie. 'If you take an abandoned quarry, though, you have to be quick if you want to develop it. Otherwise it will turn into a Site of Special Scientific Interest.'
It is a strange paradox that nature will colonise even deeply contaminated land. Until three years ago the rare black redstart, known as the 'bombsite bird', nested at the Government's model brownfield site, Greenwich peninsula. Before the New Millennium Experience got to work cleaning up the derelict, polluted former-gasworks, it had been an ideal habitat for the birds.
The redstart's post-industrial urban refuge, and other brownfield locations like it, have become increasingly important to the existence of marginalised plant and animal species. Agrochemical-intensive farming has played havoc with countryside ecosystems in the UK's green areas, dramatically reducing biodiversity. And, just as the deputy prime minister and his Urban Task Force are championing brownfield development as the path to urban renaissance, there are voices for an alternative action plan. Carry on covering the greenfield and encourage the greening of the brown, they cry.
Between 4.4M and 5.3M new homes are needed in the next 20 years, and the Government wants 60% of these to be built on brownfield land.
But demographically, demand for new housing is concentrated in the south east and the Thames corridor, where the service and information technology sectors are still creating jobs. Much of the brown land earmarked for a change of use, by contrast, is in areas with broken economies and soaring unemployment.
Southern England has brownfield sites, but not enough to absorb the projected regional population boom. Director of consulting engineer Battle McCarthy, Chris McCarthy, says there is a case for preserving and enhancing many of the self-established ecosystems that have grown up on urban brownfield sites. Well-planned, environmentally attuned new towns and villages should then be built on comparatively sterile farmland.
Under the European Union's Common Agricultural Policy farmers are subsidised for taking land out of production at the same time as they are guaranteed prices for the crops they produce. So called set-aside land can be returned to cultivation at any time, so rarely goes wild. Meanwhile, land in use is worked ever more intensively: whatever it yields the EU will buy.
From an ecological perspective, McCarthy argues that the medium-density house and garden urban pattern, beloved by the English, supports far greater species diversity than fields of monoculture crops or steroid-enhanced bullocks. And the suburban formula can be improved upon.
Cambourne, a 15,000-home Cambridgeshire new town planned by Terry Farrell Architects with Battle McCarthy and under development by Alfred McAlpine, will be extensively planted with native flora to give nature a head start. As plants mature the scale of the animal life they support will grow, both in numbers and in size.
Surface water run off from roads will be collected and filtered into ponds and marshes, supporting aquatic flora, reed beds and its own fauna. Low energy buildings will have turf roofs to maximise green surface area. And CAP set-aside land will be used to cultivate willow coppice, feeding a local biomass-fuelled power plant. Cambourne promises a townscape full of nature in place of 'lipstick landscape', says McCarthy.
Cambourne-style development should not have too great an impact on south east England's already heavily populated landscape, and by encouraging a mix of work, retail, leisure and living space, it is hoped that car use can be minimised.
Car emissions can be countered, though, by leaving brown-field sites in other parts of the country to develop their own plant life. Alternatively, these relatively low value areas can be used to cultivate forests, says director of Northern Woodlands, Mark Carey.
Mature woodland far out-performs arable land in pursuit of 'carbon neutrality' - the absorption of CO2. Carey says soil quality on many brownfield sites lends itself to cultivation of mixed conifer-deciduous plantations.
The growth of trees helps with removal of contaminants from ex-industrial land and with balancing soil pH. Their slow rate of maturation is naturally paced to organic rates of contaminant breakdown. And after 20 years, conifers can be commercially harvested.
Meanwhile the remaining deciduous woodland develops a complex, biodiverse ecology. It has amenity value - people will be attracted to it and use it recreationally - and it helps suck up the pollutants exhaled by industry and cities.
Precisely the same argument goes for well-established, biodiverse brownfield sites in inner cities. Official urban parks and green space 'work' less hard, per hectare, than ad hoc, unregulated green accidents. Giles Dolphin, planner for land use at the London Planning Advisory Committee, notes that 'green accounting' is just starting to emerge as a development issue. 'It's a concept in which environmental improvement offers a long term payback, not necessarily hard cash,' he says.
For green accounting to work the site must be a public amenity, and payback can only start when people have access. This can generate its own problems - over-use and erosion. But if effectively developed, wild urban spaces could help combat urban alienation and contribute to the psychological and physical health of city dwellers.
'As compensation for the stressful life we lead, there is a need to seek out green and peaceful breathing space, and that search for solace often leads to urban wild space. Much of this benefit is subliminal - we just feel better,' says environmental consultant Chris Baines.
If Baines sounds like a tree-hugging crank, a glance back at the changing history of planning policy suggests that decision-making has seldom been purely scientific. The UK's popular and political preoccupation with conservation in the last decade is in large part emotional and aesthetic.
It is in such a framework of scientific pragmatism mixed with touchy-feely sensibility, that the Environment Agency has started greening the banks of the river Thames, replacing hard edges with soft, and building terraced planting beds around the Greenwich peninsula. The Highways Agency, alongside projects to re-house bats and help animals cross roads safely, is the UK's largest planter of native trees after the Forestry Commission. And Railtrack is starting to cultivate plant and animal diverse habitats on its embankments and verges.
McCarthy believes that in the long term, with good planning and a supportive political agenda, a tracery of naturally vegetated brownfield sites and transport corridors could be woven throughout the UK's cities.
His case for continued green-field development and nurturing of biodiversity on select brownfield sites will grate with the thinking of the moment, however. Chief executive of the Urban Villages Forum and Urban Task Force expert David Lunts says: 'It's true that some brownfield sites have become quite rich in their own flora and fauna. That sounds like the kind of thing that trips from people's tongues at dinner parties, though.'