Now the National Housing and Town Planning Council, having perceived an existing housing shortage of around a million homes, has released revised figures estimating that 5.5 million new houses need to be built in the same 25-year period.
You may get the idea from all this that England is undergoing some kind of population explosion, but this is not the case - the numbers are growing relatively slowly. It is the household pattern that is changing, with an ageing population meaning more adults and fewer children living at home with them. People are also living longer, which means fewer homes coming on to the market; and there is a steady rise in the number of divorced and single adults choosing to live on their own.
But is it right that because the family unit is shrinking, the Government should allow building development to spread over the countryside? Mr Gummer's hope was that 60 per cent of the new housing could be built on re-used land - the so-called "brownfield" sites - leaving more than 2 million plots to be found in greenfield locations
Roger Humber, chief executive of the House Builders' Federation, thinks the problem has been overstated. "Around 50 per cent of new homes are already being built either on brownfield sites or as conversions in existing properties," he says. "And remember, some brownfield sites are actually in the countryside - places such as disused airfields - where development can represent an environmental improvement." Mr Humber points out that, in any case, the figures represent the building of only 200,000 homes per year, which is not large by historical standards.
But Dr Simon Festing, housing campaigner for Friends of the Earth, is adamant that the plans should be opposed. "Friends of the Earth has no opinion about people choosing to live on their own," he says. "But the choices they make about their housing must be sustainable ones." Building in the countryside, according to Dr Festing, means increasing levels of road traffic. "Transport and housing are inextricably linked," he explains. "If you build homes without associated transport networks, which is what happens when you build in the countryside, then people will need to travel by car, and that is unsustainable development."
Friends of the Earth co-ordinated yesterday's Halt Greenfield Housing conference along with Alarm UK, a network of anti-roads groups. FoE would like to see at least 75 per cent of the proposed housing go up in urban areas with existing transport links.
In most inner city areas there are tracts of waste land, many the result of departed industries. So why can't these urban eyesores all be regenerated by building homes? The answer is that, for several reasons, builders prefer greenfield development.
David Miller, a south London house builder, explains: "Brownfield sites are full of unexpected obstacles. Excavation and foundation work is more difficult. You don't always know for sure where the drains and water pipes are, and if you disturb a gas main the job can be held up for days. One of my digger drivers dug up a Second World War bomb once - the shock kept him off work for a week."
The extra costs of dealing with contaminated land are also a factor. Apart from the hazards of carcinogens such as asbestos and motor oil, and the dangers of methane seeping up from buried rubbish dumps, a surprising number of other common substances are now classified as contamination. Clinker from boilers and domestic coal fires, for example, was sometimes used to make-up soft ground by Victorian builders - we now know that this contains lead, cadmium and other hazards. Any builder finding such contaminants is faced with the expense of digging out the offending area and importing replacement soil from elsewhere. Combined with the new landfill tax, such measures can add up to pounds 2,000 to the cost of a new house. On heavily contaminated sites the cost of cleaning up can even exceed the value of the land.
Brownfield sites can pose other problems for builders. An infill development in a town, for example, will have the restrictions of existing roads and sewage systems, and the problem of fitting gardens and car parking spaces into the "footprint" of the site plan. The process needs careful thought and design, which may involve extra architects' fees as well as negotiations with local authority planners. Greenfield development, in contrast, can be a breeze - roads and drains can be laid out to suit the houses, and almost any house design can be used straight off the shelf.
In fact, it is the uniformity of recent rural housing that has led to much of the criticism. David Oliver, district architect for West Dorset district council, speaking at a conference last year, said: "Unless we can demonstrate that new building can be accommodated without detriment to small communities and without damage to the character and local distinctiveness of existing settlements, then we must expect that existing communities will resist all development proposals." Mr Oliver's district includes Poundbury, the Prince of Wales's pet project, which attempts to integrate modern development with rural character, and where negotiations with the planners have led to greater population densities and closer integration of homes with shops and workplaces, to cut down the need for car travel to the nearest town.
Whether Poundbury has succeeded in these aims is still being debated. Quentin Pickard, an architect and conservation specialist, says: "Poundbury is a mockery of traditional village design, with its dinky pitched roofs and gables. And there is far too much variation in materials - most traditional villages have a far more limited range of materials and house types. Too much icing spoils the cake." Mr Pickard is also scathing about Poundbury's supposed non-reliance on the car; he feels the whole village is designed around its road system, and that the accommodation caters mainly for car-owning families.
Car parking has become one of the most important planning factors. Older towns and citieshave been unable to cope with the requirements of millions of parked cars. It was not until the 1970s that developers adopted garages and off-road parking spaces as standard. Now, as though making up for lost time, car parking has come to dominate housing design.
Simon Festing is critical of the way parking provision restricts housing associations trying to convert Victorian houses into flats, and so house more people in existing inner-city buildings. Local authorities can require each converted flat to have parking for two cars. Where a large house is converted into three flats, this would mean six spaces. If the only available parking is in the street then permission to convert can be refused.
The link between housing and transport looks set to enliven this debate, and the threat of direct action against house building will not be one the new Government will enjoy dealing with.