John Prescott's plans to create more homes are "environmentally reckless" and based on "flawed maths", says the Tories' local government spokeswoman.
Mrs Spelman says people's gardens are at risk
Caroline Spelman says the deputy prime minister's scheme to build more houses in the south east amount to "a Soviet- style central building plan".
She told the party's conference in Blackpool that Mr Prescott did not understand the value of green spaces.
"To say the whole scheme is crude would be unduly flattering," she said.
More than 120,000 new homes are to be built in Kent alone over the next 20 years but Mr Prescott is concerned the process is too slow and too expensive.
However, environmentalists are worried green fields will be built on to meet demand.
Mrs Spelman warned conference representatives that now even back gardens were now being classed as brownfield sites to be fast-tracked for development.
"Farmland is being downgraded to make it easier to build on and every year 2,500 acres of green belt are buried under concrete," she said.
The Conservatives understood there was of course a need to create more homes, especially affordable ones, she said.
"But Mr Prescott you cannot be serious that a Soviet-style central building plan is the best way of delivering this?" she said.
'Concreting over the south'
"What if there is a crash in house prices? Will we then see the compulsory purchase and demolition of properties in a bid to drive prices back up?
"The whole scheme is based on flawed maths, flawed logic and a flawed understanding of just how much people value the green spaces around them."
Mrs Spelman said that while the government "concentrates on concreting over the south", it is "missing the opportunity to spread economic growth and prosperity" throughout the rest of the country.
"The government's approach to development is environmentally reckless on one hand and socially negligent on the other."
Mrs Spelman also claimed the Tories could be thanked for the government's U-turn over council tax revaluation.
Last month Local Government Minister David Miliband said the revaluation of around 22 million properties in England would be postponed until after the next election.
Mrs Spelman said her party had fought to scrap the plan at the general election in May.
"That climb-down will save seven million households £267 every year - so don't let people tell you that being a party of opposition means you can't make things happen," she said.
She pledged to attempt to reverse plans to move homes in Wales up a band next April, during debate on the legislation required to postpone the English revaluation.