David Cameron's manifesto pledge to dramatically extend Margaret Thatcher's right-to-buy policy was this morning attacked as a 'deeply unfair' bribe which will cost taxpayers billions of pounds. In a bold pitch to working class voters, the Prime Minister said the Tories would offer discounts of up to 70 per cent to  1.3million families in housing association properties to buy their home. But the National Housing Federation said the subsidy - which will be funded by forcing councils to sell off their most expensive properties - will cost taxpayers £5.8billion and was effectively worth £100,000 to each family who benefited. Scroll down for video . Thatcher's plan: Prime Minister David Cameron will announce an extension of the right-to-buy scheme which will allow all 1.3million families in housing association properties to buy their home . The Chartered Institute of Housing, meanwhile, said the move would do nothing to tackle the housing crisis - and could even make it worse by cutting the number of low-cost social homes available for poor families. Labour jumped on the remarks this morning, claiming the policy had 'unravelled' and pointed to figures showing that last year just 479 council homes were sold off – raising £100million, or 2 per cent of the funds promised by the Tories. But the Home Secretary Theresa May defended the policy on the BBC this morning – insisting it was affordable and would give families the opportunity  to live in a home that they owned. She said: 'It is a very important policy because it shows what sort of government a Conservative government would be. It shows that we're a government that's on the side of working people who want to get on a build a better future for themselves and their families.' Unveiling the Conservative manifesto this morning, Mr Cameron declared the 'dream of a property-owning democracy is alive'. He said: 'The next Conservative government will extend the right-to-buy to all housing association tenants in this country – 1.3million extra families – a new generation given the security of a home of their own.' Original plan: The right-to-buy scheme became Lady Thatcher's most famous single policy . The pledge to extend right-to-buy, which was introduced in 1980 but has now been stopped in its tracks by Labour in Wales and the SNP in Scotland, will delight the Tory faithful, who were buoyed last night by a six-point poll lead over Labour. But the policy was branded 'deeply unfair' by housing associations and industry experts today. National Housing Federation director Ruth Davison said the extension of Right to Buy to housing association properties was 'the wrong solution to our housing crisis'. She said: 'A very conservative estimate of this policy puts the cost to the taxpayer of at least £5.8billion. 'Following 40 years of successive governments' failure to build the homes the country needs, soaring rents and house prices and the biggest baby boom since the 1950s, ensuring that there enough homes today and tomorrow must be our nation's top priority.' She added: 'Halfway through a programme of austerity and in the grips of a housing crisis, if you had £20 billion of taxpayers' money, would you just give it away as a gift to some of the most securely housed people in the country on some of the lowest rents?' Gavin Smart, deputy chief executive of the Chartered Institute of Housing, said the move would do nothing to tackle the housing crisis. He said: 'In fact it could make things worse for people on lower incomes who are already struggling to access a decent home at a price they can afford. 'Individual tenants might benefit from the opportunity to own a home, but we would be very concerned that it would result in a dramatic loss of vital social and affordable housing. 'The Conservatives say that forcing councils to sell off their most valuable properties would fund this extension plus 400,000 new homes over five years – we fear the figures simply won't stack up.' Samantha Cameron and Chancellor of the Exchequer George Osborne listen to Prime Minister David Cameron as he unveils the Conservative party manifesto in Swindon this morning . He added: 'And it could have a huge impact on councils' ability to build new homes, particularly in more expensive areas like London and the south east, where it might actually make more sense for them to borrow against the value of these properties so they can fund more homes.' Senior Tory figures, including Iain Duncan Smith, Boris Johnson and David Davis, have been calling for the measure to be at the heart of the party's manifesto. The original right-to-buy saw more than 1.5million council homes being sold off at discounted rates. Leading to a surge in home ownership, it became Lady Thatcher's most famous single policy. Labour's shadow housing minister attacked the Tory policy today . The Coalition government has already increased right-to-buy discounts for council homes, meaning more are moving into the private sector. But most tenants living in homes provided by housing associations – not-for-profit bodies that have gradually replaced councils as the main providers of social housing – do not qualify. Enabling them to buy their homes is expected to require major changes to the 1996 Housing Act, and is likely to be fiercely opposed by housing associations themselves. As well as promoting home ownership, the scheme could also dramatically reduce the vast housing benefit bill. Currently, taxpayers subsidise the housing costs of many unemployed and lower paid workers who live in housing association properties. The 1.3million housing association homes are occupied by 2.75million people. Mr Cameron said: 'At the heart of this manifesto is a simple proposition. We are the party of working people, offering you security at every stage of your life. 'If you're a young person looking for training, if you're looking for a decent job, if you want to buy your own home, if you're raising a family and need help with childcare, if you fall ill, and need to rely on our NHS, if you are reaching retirement, and want real security. We are there for you – offering security at every stage of your life.' Some Labour figures, including former welfare minister Frank Field and former Cabinet minister Alan Milburn, have previously championed the idea of extending the right-to-buy to housing associations. How does right-to-buy work? Introduced in 1980, it gives council house tenants discounts to buy their home. Labour dropped its opposition to the policy but, in 1999, Tony Blair's government cut the top discount from £50,000 to £38,000 and sales slowed. What has the Coalition done? It has sought to reinvigorate the scheme, cutting from five to three the number of years tenants need to have been in a home before they can buy it and upping the discounts to a maximum of £77,000 for most areas. Are housing association tenants covered? Housing associations – autonomous, not-for-profit bodies that receive public money and loans from the private sector to provide low-cost homes – are largely exempt. However, around 800,000 HA tenants have a limited 'right to acquire' with discounts capped at between £9,000 to £16,000. The other 500,000 tenants lack any right to buy. What are the Tory proposals? They would legislate to give all housing association tenants full right-to-buy. Tenants in houses would get a 35 per cent discount, increasing by 1 per cent for every extra year they have been a tenant. Those in flats will get a 50 per cent discount, going up 2 per cent every year. Discounts for houses and flats would be capped at the lower of 70 per cent or £102,700 in London and £77,000 across the rest of England. How will this be paid for? The Tories say they will make councils sell off expensive properties when they become vacant. Council homes that rank in the most costly third of all properties of that type in their area will be sold off. Around 15,000 such properties become vacant each year, because tenants die or move. The sell-off could net £4.5billion a year. What about the proceeds? They will be split, with a proportion used to replace on a 'one-to-one' basis the council homes sold off. The new properties would be more affordable, probably in less expensive locations, and could be built either by a council or housing association. Another slice of the proceeds would be used to fund the new right-to-buy discounts for housing association tenants. The rest would go to create a £1billion fund, enabling councils to bid for cash to develop brownfield land for housing. It would enable them to clean up derelict or contaminated land, and could lead to 400,000 new homes in five years, Tories say.
David Cameron announces extension to right-to-buy housing policy . PM promises to extend  Right to Buy to all housing association tenants . Discounts of up to 70% to allow 1.3million families to buy their home . National Housing Federation said the subsidy will cost taxpayers £5.8bn . Claimed it was effectively worth £100,000 for each family who benefited . But the Tories said it would be funded by making councils sell off homes .