By William Schomberg and Estelle Shirbon
LONDON, Sept 28 (Reuters) - Britain's prime minister launched a critical week for his party's run-up to the 2015 elections by unexpectedly bringing forward the launch of a mortgage guarantee programme that critics say risks stoking a housing bubble.
Conservative leader David Cameron said on Saturday that the plan would be up and running next week, three months earlier than previously planned.
The "Help to Buy" plan is aimed at people who have been frozen out of the property market by the soaring size of deposits required to get a mortgage.
"Young people who've got a decent job and have got decent earnings - they cannot buy a house or a flat, because they have to have a 30,000-pound ($48,400), 40,000-pound or 50,000-pound deposit," Cameron said in a statement.
"Now, if you haven't got rich parents, you can't get that sort of money. So we're going to launch the Help To Buy Scheme - it's not coming in next year, it's coming in next week, because I'm passionate about helping people who want to own their own flat or home."
The initiative involves the government providing 12 billion pounds in guarantees to encourage lenders to provide mortgages of up to 95 percent of the value of properties being bought.
It had been due to launch in January and key details such as the fees banks will pay to participate have yet to be announced.
Cameron's announcement comes on the eve of the start of the Conservative Party's annual conference in Manchester. Such occasions are used by British political parties to make eye-catching announcements and this year offer the chance for them to set out their programmes before a general election due in 2015.
Earlier this month, opposition leader Ed Miliband said a government run by his centre-left Labour Party would freeze energy bills for 20 months, a move aimed at winning over British voters, many of whom have seen their living standards fall during the slow economic recovery from the financial crisis.
Signs that Britain's economy is on the mend had boosted the Conservatives' standing among voters, but Labour's support has risen in opinion polls since the announcement by Miliband. A YouGov poll for the Sunday Times puts Labour at 42 percent, with the Conservatives at 31 percent. Cameron's coalition partners, the Liberal Democrats, languish at 9 percent.
CONCERNS IN THE COALITION
Seeking to give a boost to homeownership carries risks for the government. Since the mortgage guarantee component of Help to Buy was announced in March, house prices have picked up, raising questions about whether it is still needed.
Britain's business minister, Vince Cable, a Liberal Democrat, has expressed his concerns about the programme.
House prices rose at their fastest pace in more than three years in September, one set of housing data showed on Friday. In London, prices have jumped by nearly 10 percent over the past 12 months, although other regions have seen barely any increase
In a nod to the concerns about a new boom, Britain's finance minister, George Osborne, last week asked the Bank of England to keep a closer eye on the impact of Help to Buy.
Both Osborne and Bank of England Governor Mark Carney have pointed to activity in the housing market that is well below its pre-crisis peak as a sign that there is no new housing boom.
Ed Balls, Labour's would-be finance minister, responded to Cameron's announcement on Saturday by saying the government should bring forward investment to build more affordable homes, denouncing what he said was the lowest rate of house-building since the 1920s.
"Unless David Cameron acts now to build more affordable homes, as Labour has urged, then soaring prices risk making it even harder for first time buyers to get on the housing ladder, Balls said in a statement.