At stake is unspoilt land south of Reading, protected for the past 20 years by the M4 'strategic barrier'. Private developers want to build 2,500 homes at Grazeley, a village of fewer than 100 people. Local people say if the development is allowed to go ahead, it will eventually expand into up to 30,000 homes, swallowing acres of green fields and transforming some of the most pleasant country west of London into a polluted, uncontrollable conurbation stretching 15 miles from Reading to Basingstoke.
Thirty-two parish councils have joined the Council for the Protection of Rural England's fight against the proposals, which they say breach the government's commitment to allow house building on greenfield sites only as a last resort. The planning authorities, however, need to find homes for thousands of people drawn to the area by 'Silicon Valley' - the ribbon of hi-tech and computer-related industries along the motorway from west London almost to Bristol.
The Grazeley application is seen as a test case and any breaching of the M4 cordon could have enormous consequences for other proposed developments on rural sites.
One of those fears has already come true. Berkshire CC was dismantled this year into six unitary authorities. Campaigners say this has left them without a powerful enough voice in local government to fight their cause, despite the support of most local MPs, including shadow trade and industry secretary John Redwood.
The inquiry, which is expected to last at least a year, is seen as a test of the deputy prime minister John Prescott's declaration that 'it is our firm policy to protect our countryside ... by maximising the use of recycled land'.
Action group chairman Tony Wiseman said: 'When the county council existed, it opposed all developments south of the M4 at Reading because there were no significant towns or even large villages all the way to Basingstoke. The proposed development is simply not viable in terms of schools, infrastructure or profit from the land. It will inevitably grow to as many as 30,000 homes in an area which already has serious traffic problems.'
Tony Burton, of the CPRE, said the creation of 'Readingstoke' would encourage more people to move out of London, but the development would destroy the rural surroundings they sought.
Wokingham DC, the planning authority, is obliged under the 1995 Berkshire Council Structure Plan to find space for the new homes. Two alternative sites have been proposed but they too are in the 'protected' zone south of the motorway.
The council's chief planning officer, Chris Wood, said: 'Although the council would rather see no major development of this size south of the M4, we have been forced by the structure plan to choose the site where we feel this number of houses could be accommodated best with the necessary community facilities and transport infrastructure. It is a case of us trying to make the best of a bad situation.'