David Cameron is to defy warnings of a new housing bubble and bring forward controversial state-backed mortgages as part of efforts to show the Tories will tackle the rising cost of living - three months earlier than planned.
The second stage of the Help to Buy scheme - allowing people to acquire a property with a deposit of just 5% - will begin next week, the Prime Minister revealed.
Liberal Democrat Business Secretary Vince Cable warned the scheme "could inflate the market" and said he feared there was a "danger of getting into another housing bubble".
Mr Cameron said it was not right that young people with decent jobs but without "rich parents" were being frozen out of being able to buy a home.
It is one of several measures - including a tax break for married couples and extended cancer drug funding - being announced as Conservatives gather in Manchester for their annual conference.
The party will also use the event - under the theme "For Hardworking People" - to announce a ban on "slap on the wrist" cautions for serious offences and help for armed services personnel to buy homes.
Mr Cameron told the Sunday Telegraph he recognised his party "have to do more to explain how we are going to help people with the cost of living" - an issue Labour has made its central theme.
Help to Buy was launched earlier this year for newly-built properties and was due to be extended to existing homes worth up to £600,000 from January.
It has caused tensions within the coalition administration, with Liberal Democrat Business Secretary Vince Cable among those raising the alarm about over-inflating prices.
With new figures showing the fastest rises for three years, Chancellor George Osborne has sought to calm fears by saying the scheme will be reviewed annually by the Bank of England.
But Mr Cameron insisted big increases were mainly limited to London and said he was determined to press ahead more rapidly.
"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, £40,000 or £50,000 deposit," he said.
"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."
Shadow chancellor Ed Balls questioned why first-time buyers needed a scheme that covered such expensive properties and said extra housebuilding was the key to helping people afford a home.
The Prime Minister's party is in relatively buoyant mood as the economy shows signs of recovery but the latest opinion polls suggest a significant post-conference boost for Labour.
A YouGov survey for the Sunday Times gives Labour a healthy 11-point lead over the Tories by 42% to 31%, with Ukip on 13% and the Liberal Democrats 9%.
With some Tory MPs openly suggesting an electoral deal with Ukip may be required in 2015, a poll of Conservative local councillors found almost a quarter (24%) backed the idea.
Ukip leader Nigel Farage is due to speak at conference fringe debates.
But Mr Cameron said that while he wanted to "win back" voters from the eurosceptic party, "I'm not chasing off to the Right, I'm very firmly anchored where I have always been."
He was a "modern compassionate Conservative who believes that there is a very important role for government in making sure that we look after the poorest in our society, that we are a compassionate society, that we give people opportunities who aren't necessarily born with them", he said.
"We are not going to abandon that."
Conservatives will begin the conference this afternoon with a tribute to the party's former prime minister Baroness Thatcher, who died earlier this year.Suggest a correction