The Tories’ rent to buy scheme, which will allow “generation rent’ first to live in their homes at a 20% discount and then buy them at 20% under market value, would be aimed at the under-40s.

Speaking on the eve of the Conservative party conference in Birmingham, David Cameron said: “I want young people who work hard, who do the right thing, to be able to buy a home of their own.

“So these starter homes will be sold at 20% less than the market value.

“They can’t be bought by foreigners, they can’t be bought by buy-to-let landlords, they can’t be flipped round in a quick sale. They can only be bought by hard-working people under the age of 40.”

The £400m plan is designed for single people earning up to £33,000 and couples on up to £66,000.

Housing associations would share a pot of £400m of cheap government loans to build 10,000 homes on brownfield land over two years, between 2015 and 2017.

The tenants could live there for seven years before being able to purchase them. Alternatively, they could simply move out and buy or rent elsewhere.

If the home is sold, the provider can use the proceeds to build more affordable homes in their area.

If it is not, the home will still be available for someone else to “rent to buy”.

Under the scheme, housing associations will have up to 16 years to pay back their low-cost loans. Until these are repaid, the homes would have to be available at below market rents.

Half of the funding is for London.

However, the move is being seen as a cynical vote-getter. Floods of comments online include: “There is a general election coming up! They would say they will GIVE you a house if they think it will gain votes!”

There have also been calls for more detail.

Stuart Ropke, of the National Housing Federation, said: “We welcome any measure which can help to accelerate the supply of new homes.

“However, we still need more clarity about what the policy aims to achieve. We are concerned most tenants will be unlikely to be able to afford to buy after seven years and we need to consider how we will meet their long-term housing needs.”