David Cameron has defended moves to bring forward a state-backed mortgage scheme and said he had several major lenders signed up to take part.
The second phase of the controversial Help to Buy scheme is being launched next week, three months ahead of schedule, as part of Tory efforts to show they are tackling the cost of living.
Speaking as activists gathered in Manchester for the start of the party conference, the Prime Minister dismissed fears the move could provoke a new house price bubble.
He also ruled out any government he leads after 2015 introducing a mansion tax on expensive properties - a clear signal to the Liberal Democrats of a potential red line in coalition negotiations.
Taxes on wealth were "not sensible for a country if it wants to support wealth creation, wants to reward saving and people who work hard and do the right thing", he told BBC1's Andrew Marr Show.
Help to Buy was launched earlier this year, enabling people to buy newly-built properties with 5% deposits 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 price.
But Mr Cameron said he was right to press ahead to help young people without rich parents get on the housing ladder. He added: "Don't take it from me, take it from the Bank of England.
"We asked them last week for their assessment of the housing market and they said expressly that there isn't a bubble.
"I am not going to stand back while people's aspirations to get on the housing ladder, to own their own flat, to own their own home, are being trashed.
"That is why we need to act and that is why it is good news that we are bringing forward the Help to Buy scheme.
"I can tell you today that NatWest, RBS, Halifax, are all going to be putting forward these products.
"This is not something totally new in our country - for most of our lifetimes it's been possible for people to go out and buy a flat with a 10% deposit.
"If we don't do this, it will only be people with rich parents who can help them with the deposit who can get on the housing ladder.
"That is not fair, it is not right, it is not the sort of country I want to live in."
Asked about the mansion tax - a long-cherished Liberal Democrat policy which Labour is also committed to - he told the programme: "I don't think this is a good idea.
"I want to live in a country where people work hard, they save and they put money into their homes. I think it's right people pay council tax, it's right people pay stamp duty - and we put that up - but to go after someone's house every year with a wealth tax, I don't think that's a sensible thing to do.
"I have never been in favour of this idea. I think it's a bad idea."
Asked if voters could be sure that there would be no mansion tax if he was Prime Minister after the next election, Mr Cameron added: "That's correct. Stamp duty yes, council tax yes, but I think wealth taxes are not sensible for a country if it wants to support wealth creation, wants to reward saving and people who work hard and do the right thing."
Mr Cameron said the key to tackling the cost of living was staying the course with the Government's efforts to sustain the economic recovery, create jobs, cut the deficit and lower taxes.
He conceded that was " not enough" on its own though as he seeks to counter Labour leader Ed Miliband's popular promise of a 20-month freeze on energy bills which has helped boost Labour's opinion poll ratings.
But he said that on the issue it was better "to tackle the disease rather than the symptoms" by making the market more competitive and forcing firms to put customers on the lowest tariffs.
He attacked Mr Miliband's policies as "nuts".
He added: "When you take his approach as a whole, it is anti-business, it is anti-enterprise, it is saying to companies that are investing in Britain: I am going to put up your taxes - take the jobs somewhere else.
"That is absolutely the wrong approach.
"It is nuts frankly to put up corporation tax. Jaguar Land Rover is now making world-beating cars, selling them all over the world and Ed Miliband wants to put up their taxes. That is nuts."
Asked if he was saying the Opposition leader was "nuts", he added quickly: "I don't want to get into a huge argument with the mental health lobby."
Mr Cameron denied the Government was failing to deal with fast-rising energy bills.
In a direct riposte to Mr Miliband's proposal, he said: "I want low prices not just for 20 months, I want them for 20 years, so what we need to do is go to the reasons they are going up in the first place."
The price freeze promise "unravelled within about 12 hours when the next day he said he might not be able to keep his own promise", Mr Cameron said.
"We have got to make these markets more competitive, we have got to make sure the companies behave properly and put people on the lowest tariffs and we are legislating for that."
He also said he would "look at all the subsidies" amid hints that state help for renewable energy schemes could be scaled back to help reduce domestic prices.
"Is this enough? No. We need to look at all of these markets and make sure they are working for herd-working people."
Polling commissioned by Labour found most voters want Mr Cameron to implement a freeze now on energy bills - underlining the popularity of the Opposition proposal.
YouGov also found 47% of adults believe the Prime Minister will defend the interests of energy companies while just 20% back him to stand up for the public.
Energy companies have warned the move could leave Britain facing blackouts - claims dismissed as ''scare stories'' by the Labour leader and not believed by 83% of voters.
Mr Cameron told Marr: "I'm not complacent about our recovery. We have a long way to go.
"We have a huge deficit still to pay down. Labour's debt crisis isn't over and the debt crisis is linked to the problems of the standard of living.
"That's why I want to help people get that first apprenticeship, that first job, that first home, start up that first business. But we need to get business to invest.
"Bashing and taxing business is going to cost us jobs, set us back and make sure our economy is weaker."
He went on: "In the end we have to make the big argument about living standards, which is the only way to sustainably raise living standards is to keep the recovery going - and the economy is now moving, to keep on creating jobs - and we are creating those jobs, to keep on cutting the deficit because that keeps interest rates and, crucially, mortgage rates low and to keep on cutting people's taxes because that is the way to give people more of their own money to put into their pockets to spend as they choose."
Shadow work and pensions secretary Liam Byrne said there were "big questions" that remained over the second stage of the Help to Buy scheme.
He told Murnaghan on Sky News: "I notice the Prime Minister deliberately excluded London from his claims this morning. House prices in London are growing at 10%. That feels to me like it is not sustainable.
"So what we are saying is let's get the Bank of England to look at the details of this scheme and let's ask them to opine on questions like why is the cap being set at £600,000? Is that too high?
"So I'm afraid there are big questions that need to be answered especially when you look at the property market in London."
Other measures already announced as the conference gets under way include a £200-a-year tax break for married couples from 2015 - the realisation of an eight-year-old promise by Mr Cameron during the Tory leadership contest which will please activists.
There will also be an extension of cancer drug funding, a ban on "slap on the wrist" cautions for serious offences and help for armed services personnel to buy homes, Tory ministers have announced.
Chancellor George Osborne repeatedly declined to say whether Mr Cable had been consulted about the acceleration of the Help to Buy scheme.
He told Pienaar's Politics on BBC Radio 5 Live he was "determined not to repeat the mistakes of the past" by allowing house prices to overheat the wider economy.
But he dismissed concerns about a bubble as London-centric, saying the idea of a boom would seem "very, very remote" for people in parts of the north west where prices had been falling.
Mr Osborne defended the marriage tax break - which allows around a third of wedded couples including same-sex partners but excluding higher-rate income taxpayers, to transfer allowances between them.
It has come under fierce attack from Labour, the Liberal Democrats and single parent and other campaign groups for prioritising one family structure against all others.
Mr Osborne said: "This is a sensible, straightforward way of saying we as a society are committed to marriage. It's not about being judgmental; it's about doing the right thing for society."
He denied claims - in a new book, In It Together by Matthew d'Ancona, serialised in The Daily Telegraph and The Sunday Telegraph - that Mr Cameron opposed the mansion tax because it was unacceptable to wealthy Tory donors.
The Chancellor added: "That is just not true. David Cameron has been against the mansion tax ever since I've known him, long before he was ever having to deal with any donors."
Contesting Labour claims that the party was overseeing a recovering benefiting mainly the best-off in society, Mr Osborne said new figures showed the richest now paid "a greater proportion of income tax revenues in this country than at any single point under the last Labour government".
Shadow business secretary Chuka Umunna said: "British business needs a government that understands it.
"David Cameron is so out of touch he doesn't seem to understand that the 2.4 million businesses that are losing out from our broken energy market are what matters.
"While he thinks all that matters is cutting taxes again for the 80,000 biggest businesses that pay corporation tax, Labour knows the priority for Britain right now is cutting the business rates for the owners of 1.5 million shops, pubs, workshops and start-ups.
"It's time for Britain to back our businesses once again and only a One Nation Labour government will make that happen."
Mr Osborne said addressing the cost of living was not about "gimmicky government interventions" that would be wiped out if the economic recovery faltered.
"Ultimately what really matters is whether you have a job, whether the economy s growing, whether you can afford a home. These are the big picture issues," he added.
Labour would "completely wipe out any gains that people have made from a series of gimmicky government interventions" if mortgage rates rose because borrowing got out of control, he said.
"Our economic plan is working, it is turning this economy around but it is also a plan for living standards because if you don't have a recovery you are not going to have any kind of recovery in living standards."
Mr Cameron rejected reports that he had already discussed with Deputy Prime Minister Nick Clegg the possibility of a future Conservative/Liberal Democrat coalition after the 2015 general election.
"Every time I speak to Nick Clegg about the next election, it starts with me telling him that my aim is to put him out of a job, and he understands that," Mr Cameron told the Marr Show.
" I don't want another coalition, I want a Conservative-only government and I think that's what's right for the country. That's what I will be going all out for in these next 20 months.
"Frankly I'm not going to speculate about anything else, because it's not what I want, it's not what I'm planning, and frankly I don't think it's what the country needs."
He added: " We've done great things, it's a radical government, but there's more we can do if we were a Conservative-only government.
Mr Cameron denied reports that he had gone through polling data ahead of the 2010 election and concluded that he could not win an overall majority for the Tories and would need to prepare for coalition with Lib Dems.
"I certainly did not do that," said the PM. "I spent my entire time trying to win that election."
He insisted that an overall majority is possible for the Tories in 2015.
"I think this next election is wide open to win," said Mr Cameron. "We have a huge battle.
"We have to persuade people who've gone to Ukip that they should come back to the Conservative Party because we are delivering for hard working people, the economy is recovering, we are on the right track.
"We have to persuade Labour voters that there used to be a home in Labour for people who were pro-enterprise but wanted good public services, but that it is now an anti-enterprise party (and they should) come over to us, the Conservatives.
"We have to persuade people who normally vote Liberal you don' t need to have a Liberal party in government in order to have a compassionate country.
"I'm absolutely in this to win it, I believe it can be done, I'm passionate about running a Conservative-only government, not for my own benefit but because I believe the country needs us to go further and faster on the things that really matter."
Mr Cameron sent a message to former Tory voters considering switching to Ukip because of their desire to leave the European Union.
"At this election we will have a very clear message, which is if you want an in/out referendum, there is only one way to get it and that is to put me back in 10 Downing Street so I can deliver on my promise," said Mr Cameron. "A vote for any other party, including Ukip won't deliver that."
He declined to discuss the details of the renegotiation of Britain's membership of the EU which he intends to conduct after the 2015 election ahead of a referendum in 2017.
But he said he was "determined" to get out of any commitment to an "ever-closer union", which is enshrined in existing EU treaties, and made clear that he expects the renegotiation to end in a new treaty.
"The phrase 'seeking an ever-closer union' is not what I want and not what the British people want," said Mr Cameron. "Other people can sign up to an ever closer union, but Britain should not be in an ever-closer union and I'm determined to get out of that.
"We need a treaty renegotiation, I'm convinced one has to happen."
Mr Cameron repeated Mr Osborne's position that a Conservative government would use spending cuts and not tax rises to complete the job of deficit reduction following the election.
"If you look at how we reduced the deficit, the richest paid 10 times more than the poorest, and that's right," he said.
"But frankly, looking ahead, if we are going to get to grips with the problems with the cost of living people face, we've got to say to people we are not going to go on putting up taxes. The rest of the deficit reduction programme that George Osborne has set out we believe we can do by continuing to bear down on spending.
"I want to see us go on helping hard-working people, particularly low-paid people, to keep more of their money to spend as they choose."
Mr Cameron denied reports that he has already written off Ed Miliband as a threat in the coming election.
"You never under-estimate anyone in politics, you never are complacent in politics," he said. "Politics ought to be competitive, that's the whole point of democracy. It keeps us on our toes and makes us work hard."
Royal Bank of Scotland, which is 80% state-owned, said it would be participating in the new phase of Help to Buy with a range of 95% loan-to-value mortgages for first and next-time buyers in the UK.
The group, which operates 2,000 branches through RBS and NatWest brands, aims to sign up 25,500 customers through the scheme and said opening hours would be extended at peak times to cope with customer demand.
Ross McEwan, head of RBS Retail, who is due to take over as chief executive of the group on Tuesday, welcomed the announcement that the mortgage guarantee scheme would be launched soon.
He said: "Despite the economy recovering, we know many families are finding it tough to get a mortgage deposit together.
"We are committed to helping as many people as possible across Britain to get on with their lives, to buy their first home, to move to a bigger house as their family grows."
After the Marr interview, Mr Cameron travelled out of Manchester to the Egerton Green housing development.
The premier met James Oliver and Emily Jones, who are buying their first home.
During a tour of their three-bed plot, Mr Cameron - who remarked he had been woken up in the night by Manchester revellers - explained the Help to Buy scheme.
Mr Cameron had a tour of the estate and climbed the scaffolding of the home Mr Oliver and Ms Jones were buying.
Following Labour's announcement that it would repeal the so-called "bedroom tax", Mr Cameron told BBC2's Sunday Politics: "Of course, a lot of policies that we've had to introduce are unpopular, but we are battling with an enormous budget deficit and a need to get that deficit under control.
"I think people want to see us reform welfare and cut the costs of welfare and to do it in a way that's fair.
"When I look at the spare room subsidy, the point I make is this - we don't subsidise people for additional spare rooms in private sector accommodation when they are on housing benefit, so we shouldn't give people extra money for spare rooms when they are in council accommodation.
"What Ed Miliband is doing is basically saying his first act as prime minister would be to spend another £1 billion on welfare, putting up our deficit - more borrowing, more spending, more debt. Exactly the things that got us into this mess in the first place."
Defence Secretary Philip Hammond insisted the Government would not increase borrowing to cover the married tax allowance reforms and said there would be "scope" to address other household financial pressures.
He told BBC Radio 4's World this Weekend: "I'm confident that we can cover it without more borrowing, which of course, is Labour's answer for everything.
"I think what we are looking at now as the economy slowly starts to recover, there will be some scope, very cautiously, to enable us to address some of the pressures the people are feeling.
"We are acutely conscious of the fact that the economy is beginning to enter a recovery phase but this will only feel real to people if they start to see improvements in their standards of living."
Mr Hammond said improving skills in the workforce was vital in ensuring that Britain can compete with emerging economies.
He added: "Yes, we want to see a high wage, high living standard economy but the world doesn't owe us a living and we have got to ensure that we succeed in this global race by, for example, improving the level of qualifications that we are getting pupils in our schools and our universities, by increasing the number of apprenticeships - half a million new apprenticeships last year."
Ben Thompson, managing director of Legal & General Mortgage Club, said: "There will of course be some surprise and even some scepticism with regard to this announcement and implementation being accelerated.
"Right now it remains unclear exactly what the scheme details and specifics are for lenders, and in that regard precisely who will participate other than RBS and Lloyds Banking Group.
"However it is clear that there are potential First Time Buyers and movers who can afford to pay a new and increased mortgage monthly payment, but are having to spend significant time saving for a substantial deposit, larger than at any time in recent decades.
"This has to be fixed in order that families can live in suitable accommodation and enjoy home ownership in the same way that previous generations have. 95% lending has simply not become high risk overnight."
He said some buyers would be able to bring forward purchases in regions where since prices were rising it was important not to delay, but said the Government should not duck the issue of housing supply.
"If the UK had an appropriate supply and demand balance, arguably many of these mortgage and housing initiatives and stimuli would not be needed," he said.