Theresa May has insisted she is not concerned about the Tory opinion poll lead narrowing as she sought to recover from a U-turn over her flagship social care reforms.
Mrs May, who has seen a double-digit margin eroded in recent surveys but still enjoys a lead over Labour, said the only poll that counts is on June 8.
But in a major set-piece interview with the BBC's Andrew Neil she was challenged over the announcement that a cap on social care costs would now be included in her plans, having previously been ruled out.
"There's only one poll that counts in any election campaign," she said.
"That's the one that takes place on June 8 when people have actually cast their votes, when they have made that choice, which is a crucial choice.
"I think this genuinely is the most crucial election I have seen in my lifetime because it is about getting Brexit negotiations right, getting the right deal for Britain from Europe and going beyond that, a plan for a stronger vision for the future."
She added: "I have never taken anything for granted in this election."
Mrs May, who repeated her "strong and stable" leadership slogan despite the reversal on social care policy, denied her manifesto was "uncosted and half-baked".
She said: "No, what we have set out in our manifesto is a series of policies which address what I see and I think are the five great challenges that we face as a country."
Mrs May sought to highlight the looming Brexit negotiations as a reason to vote Tory rather than Labour.
"There's only going to be a choice between two people as to who's sitting opposite those 27 European countries, me or Jeremy Corbyn," she said.
Challenged about the social care U-turn, Mrs May said: "What I've done today is I've seen the scaremongering, frankly, that we've seen over the weekend. I've seen the way that Jeremy Corbyn wants to sneak into Number 10 by playing on the fears of older and vulnerable people, and I've clarified what we will be putting in the green paper which I set out in the manifesto."
Pressed on how the Conservatives would pay for the promise of an additional £8 billion for the NHS, Mrs May said: "In our manifesto we've put some examples of how we're going to change the way money is used.
"On winter fuel payments, for example, we will means-test that. That money will go into health and social care."
Asked where the money would come from, she said: "What we have done, if you look at our record, is shown that we can put record sums of money into the National Health Service at the same time as we're ensuring that we're building that strong economy. And that's what we'll do for the future.
"Our economic credibility is not in doubt. It's the Labour Party who's in the dock when it comes to responsibility."
Asked again where the money would come from, the Prime Minister said: "What we will do in the future is ensure that we have the strong economy, growing economy, that enables us to generate the funds to put into our public services."
Mrs May was challenged on her previous comment that there would be "dire consequences" for Britain if the country failed to get a good deal in the Brexit talks.
"Well I've said that no deal is better than a bad deal," the Prime Minister said.
"I believe that, as I've just said, there are some people here who are willing to sign up to any deal.
"What I want to do – the reason I think, the reason I've said what you've quoted, and the reason I think this is such a crucial part of the question that underpins this election, is that we need to get Brexit right in setting the tone for the next, not just five years, but actually for the future.
"It's about our economy, it's about all the things that we want to do in terms of ensuring we work with our European partners."
She added: "What I have every confidence is that we will be able to negotiate a good deal with the right negotiating hand, with the strength of mandate behind us to take into those negotiations and that's what I want to do."
Mrs May also said she would "definitely stay for the next parliament".
"Beyond that, Andrew – I mean this is – I haven't got through this election yet. I'm focusing on this election.
"It's really important. It's the most crucial in my lifetime, it's about the future of our country and who people trust to take us forward in the future."
Mrs May acknowledged the NHS had missed "some of its targets" but insisted "targets aren't the be all and end all".
Following the Budget U-turn over raising national insurance for self-employed workers, she insisted that policy had been taken "off the table", but refused to rule out rises in future as part of her review of the so-called "gig economy".
"I have every intention of reducing taxes on businesses and working families," she said. "But I want to ensure that when we do that we're able to do that in a sustainable way."
Pressed on whether the national insurance plans could return, she said: "We need to look at how the employment market is working at the moment. That's why I'm very clear that I want to put in extra protections for workers.
"I think things are changing in the way people are being employed and we need to ensure that we recognise that and protect workers. But in all of these issues we can only do these things, we can only make sure that we're able to lower taxes, we've got the strong economy."
Challenged on the squeeze in living standards being faced by the "just about managing" families she said she wants to help, Mrs May said: "I want to see higher paid jobs in this country. Doing that is about building a stronger economy."
She refused to say how many pensioners would lose their winter fuel allowance of up to £300 under her plans to means-test the benefit.
"What we are doing is going to ensure that the least well-off pensioners will have their winter fuel payments protected, but yes we will consult. I think it's right that we take those views of people, of charities, of organisations working with older people and others, to look at where that level should be set.
"But overall in the changes that we're making and in the policies we're adopting, what I want to do and what I'm going to do is to be protecting pensioners for the future."