Former Conservative minister Michael Portillo has called on Theresa May’s government to make a dramatic intervention in the housing market and build thousands more council homes.

Speaking to Building at the Ecobuild conference in London, the former secretary of state for defence said he was “astonished” that the government was allowing a “freefall” in home ownership under its watch.

Portillo said: “I think it is amazing and shocking that home ownership is in freefall under a Conservative government. I am astonished that the Conservatives have allowed this to happen, even for reasons of self-preservation alone.

“One of the reasons that Thatcher promoted home ownership is that it promoted responsible citizens with a stake in society. But another reason was that those people would tend to be conservative. One of the great foundations of conservatism is threatened by the lack of home ownership.”

The housing white paper launched by housing minister Gavin Barwell last month heralded a shift in policy away from focussing solely on increasing home ownership to promoting other tenures, including rental.

The paper also revealed initial plans to reduce the time developers have to build on sites with planning consent from three years to two and to give councils compulsory purcase powers over sites that had planning consent but had not been built on.

But Portillo said these proposals skirted around the edges of the problem and would fail to tackle the issue of lack of homes. He added: “I know what I would do, I would build more council houses. It is the most effective and most direct intervention the government can make in the housing market. All these other interventions are indirect and are of limited effect.

“If there were more houses, demand would weaken, rents would fall, house prices would fall and more people would be able to afford houses. And in due course I would sell the houses to the council house tenants. So know what your objective is and do whatever is required to get there. The objective is cheaper houses, more houses, more home ownership.

“To do that the government needs to make a massive intervention in the housing market.

“It will cost money, I don’t know what the Treasury’s latest theology is on capital spending. In the unique circumstances that you almost assume that the Conservatives are going to win the next election I would set out the entire programme.

“I would say, yes, we are building these homes and one day council tenants can buy them.

“We have got to increase the housing stock, everything they have tried and easing the planning constraints are failing. We are now seeing a position where housebuilding is in the hands of a few builders and it’s is not in their interest to build more.”

Portillo also criticised former prime minister David Cameron and chancellor George Osborne for failing to address the crisis when they were first elected in 2010.

He said: “I am shocked that none of the young people I work with are home owners. They are all paying £800 a month for a room in a six-bedroom house sharing two bathrooms. These are middle class people with decent salaries, excellent job prospects and unless their parents die they have no hope of getting on the housing ladder [like] my own generation.

“The astonishing thing for me is that Cameron and Osborne were in office for five years and did nothing about it? To me the extension of home ownership is fundamental. It is almost a defining issue to what conservatism is about.”