Green-field developments have mushroomed over the past 10 years, not least because of the high cost of car parking in cities and towns. But if visitors to out-of-town sites had to pay a parking charge higher than that in town centres, the decline of such centres might be halted.
The imaginative use of car taxation was one of the main recommendations of the latest report of the UK Round Table on Sustainable Development, the Government's advisers on green issues. The Round Table argues that developers of green-field sites should have to pay the financial and environmental costs they impose on society.
One option is to levy a heavy surcharge for using a green-field site. Another is that all car-parking spaces on a new development should be heavily taxed, either as a one-off levy paid by the developer or a minimum parking fee for drivers.
John Adams, secretary of the Round Table, says: "This is used in several countries. It would help to level the playing field for cities and out- of-town developments."
Among advocates of compulsory car-parking charges are the environmental pressure group Transport 2000 and the Campaign for the Protection of Rural England. The idea was also floated in last year's Green Paper on transport, but the Government was clearly unenthusiastic. It was keener, instead, on the idea of congestion charges on routes where traffic is very heavy. The problem with this proposal, though, is that it would accelerate the decline of traditional shopping areas, as the urban areas are the most congested.
Consultation with local authorities has shown their enthusiasm for imposing car-parking charges on green-field sites, but there is a limit to how much a single council can achieve. Keith Gardner is assistant chief planner for the London planning advisory committee, which advises London boroughs on planning policy. "We need to get councils working together," he says.
Mr Gardner explains that so few journeys in inner London are made by car that it is not an issue there. "The problem is in outer London, where developers are holding boroughs over a barrel by threatening to go outside the M25. We are encouraging development that is not dependent on cars."
Edinburgh City Council, which is promoting car-free areas in the city, has already reached agreement with one developer to charge for all car- parking spaces as a condition of planning consent. The developer of the Leith Docks site will also pay pounds 1m into improving public transport links.
Planning professionals believe that it is essential to adopt some system of car taxation to reduce road use and make older shopping areas more attractive again. Jed Griffiths, a past president of the Royal Town Planning Institute, says: "If we are going to proceed towards sustainable development, there must be financial incentives and penalties such as a car tax and parking charges. But we have to see a collaborative approach on a city and regional basis, not just looking at single cities but across counties as well. We might see progress with a Labour government devolving power to regional government."
The alternative might be a nationally set minimum charge for each car- parking space, wherever it is. But a national or regional approach would lead to problems of definition. Friends of the Earth might be expected to be one of the strongest advocates of general car parking charges, but is sceptical about its potential.
"It is something that has to be considered, but how would it be administered?" asks Roger Higman, FoE's transport campaigner. "What is out-of-town? Would it be a levy on all car parking, regardless of where it is? Would there be a higher rate for out-of-town developments?"
These are practical questions that might generate pragmatic answers. But any government seriously interested in ending the decline of town and city will surely pay close attention to the growing debaten