(Reuters) - Tens of thousands of young Britons will be offered the chance to buy their first home with a hefty discount by Prime Minister David Cameron on Monday, a scheme he hopes will boost his re-election chances for May next year.

With less than five months to go before what is shaping up to be an unusually close election, Cameron and his Conservatives are keen to show voters that the steady economic recovery they have presided over can, if sustained, lift living standards.

Previous Conservative leaders such as Margaret Thatcher and Harold Macmillan proved that boosting home ownership was a vote winner and Cameron will present the scheme as something he is only able to do because of his government's responsible stewardship of the economy and reduction of the budget deficit.

"Under this scheme, first-time buyers will be offered the chance of a 20 percent discount, unlocking home ownership for a generation," Cameron will say, according to advance extracts of his speech released by his office.

"This is all part of our long-term economic plan to secure a better future for Britain, making sure we are backing those who work hard and get on in life."

Under the Starter Home initiative, first-time buyers below the age of 40 will be able to get a minimum 20 percent discount on 100,000 new homes to be built on under-used or unviable brownfield land.

Planning costs and levies will be waived in return for a promise from housebuilders of such discounts. Aspiring buyers will be asked to register their interest from January, six months earlier than originally planned.

Cameron's office said over 30 house builders including Barratt, Persimmon and Taylor Wimpey had already pledged their support as well as several local councils.

He will announce an 8-week consultation period for the scheme on Monday.

Finance minister George Osborne offered another housing-related pre-election sweetener earlier this month, cutting taxes on property purchases for 98 percent of home-buyers.

And last October, the government launched its Help to Buy mortgage scheme, which offers government guarantees to high loan-to-value mortgages.

The opposition Labour party criticized Cameron's plan.

"No one will believe David Cameron's promises on housing and home ownership," Emma Reynolds, Labour's housing spokeswoman, said in a statement.

"He said he would get Britain building but instead he has presided over the lowest levels of house building in peacetime since the 1920s."