The Conservatives are pledging an extra £8bn a year for the NHS in England by 2020 if they win the election.
The party said it was “absolutely confident” it could fund the five-year plan for the service, drawn up by its boss Simon Stevens last year.
Labour, which is highlighting its own guarantee of one-to-one midwife care, said the “unfunded” Conservative pledge was a sign of a campaign in panic.
The Lib Dems have also pledged £8bn, funded by scrapping some tax reliefs.
In other election news, Nick Clegg’s party is also promising new laws to protect people’s rights online including the threat of prison sentences for firms illegally selling personal information.
Last year Mr Stevens, head of NHS England, cited £8bn as the funding gap between what the NHS currently receives and what it needs to implement his modernisation programme.
Speaking on BBC Radio 4’s Today programme, Health Secretary Jeremy Hunt said there had been a “step change” in demand for the NHS due to an ageing population, and said the Tories’ commitment was “not a blank cheque”.
Asked how the Conservatives would fund the pledge, he said the economy had been turned around and pointed to investment in the service during the last Parliament, when the government guaranteed an above-inflation increase in funding.
He said: “If you want to be sceptical about the commitment, look at the track record.”
Policy guide: Health and care
This issue includes NHS funding, GP access and social care, particularly of older people.
Mr Hunt added: “We inherited an economy that was shrinking and we’re turned it around, and we’re creating now 1000 jobs every single day, and each one of those jobs is paying taxes, the new companies that are being created are paying taxes and that in the end is how you pay for an NHS.”
Mr Hunt said the £8bn was in addition to an extra £2bn committed to the NHS at last year’s Autumn Statement.
But Labour’s shadow health minister, Liz Kendall, said the pledge was “not worth the paper it’s written on” and criticised the Conservatives’ “fantasy funding promises”.
She told Today: “We are the only party that has committed additional funding to the NHS that’s properly sourced… we will do whatever it takes to get the NHS the money it needs.”
Labour has promised an extra £2.5bn a year for the NHS, to be paid for by a tax on homes worth £2m or more, a levy on the sales of tobacco companies and curbing what it says are tax breaks enjoyed by hedge funds and other finance firms.
Last month, Liberal Democrat leader Nick Clegg challenged his rivals to “come clean” on how they would fund the £8bn shortfall.
He said his party would add £2bn allocated in the Autumn Statement to funds raised by scrapping some reliefs on capital gains tax and employee share schemes, enabling it to invest £3.5bn over six years on mental health care.
Liberal Democrat health minister Norman Lamb accused the Tories of “trying to pull the wool over the British public’s eyes”.
“It’s easy to say you want to support the NHS, the difficult part is saying how you will pay for it. As Nick Clegg said, the NHS doesn’t need warm words, it needs hard cash,” he told BBC Radio 5Live.
UKIP said it had a “fully-funded plan” to put an extra £3bn into the NHS.
Scrapping the HS2 scheme, quitting the EU and reducing funding for Scotland would pay for 8,000 more GPs, 20,000 more nurses and 3,000 more midwives by 2020, it said.
According to NHS England, if spending increases in line with inflation, there will be a £30bn shortfall in the health service budget by 2020.
Analysis by Jonny Dymond, BBC Conservative campaign correspondent
It’s a day of role reversal today as the Conservatives spray apparently unfunded largesse at the NHS and Labour cries foul at what it calls irresponsible spending.
The Conservatives won’t say where the money’s going to come from, apart from “future growth”, but insist voters should look at their record, both in building the kind of economy that can support such spending and in funding the NHS over the last five years – to the tune of £7.3bn a year over and above inflation, by the end of the last Parliament.
Conservative officials also dispute that there’s any kind of change in campaign momentum; there’s been comment about the need to run a more positive campaign, with some suggestions from Team Cameron of good times to come for a long-suffering electorate.
But the Conservatives say that all week they’ve been bringing out good news for voters, and that the best news of all is a strong economy.
Its five-year plan says £22bn of the £30bn could be found through efficiencies and new ways of working.
Chris Ham, chief executive of the King’s Fund, said this would be a “huge challenge”.
Measures such as improving procurement and cutting agency costs would make a contribution, he said, adding that “every doctor and nurse” should be “fully involved” in the reforms.
Prof Ham said there seemed to be an “emerging political consensus” around the need for an extra £8bn.
“The issue is whether Labour will make this very specific commitment on matching terms and we do not yet know that,” he added.
Asked during Labour’s health campaign launch in West Yorkshire whether he would match the £8bn pledge, leader Ed Miliband said his party was making a “much more significant commitment” than the Conservatives.
“The NHS needs real money now, not phoney promises later,” he said, adding that Labour would fund the NHS “as is required”.
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