The planned hike in national insurance will go ahead in April, Downing Street has confirmed, despite mounting opposition from Conservative MPs.
A Number 10 spokesman said Boris Johnson and Rishi Sunak were “fully committed” to the rise.
Previously, the PM had stopped short of guaranteeing that the 1.25 percentage point increase would go ahead as planned.
It comes despite a report in The Times that Johnson was considering “back-sliding” on the tax rise in an attempt to placate his unhappy backbenchers.
At a Downing Street briefing for political journalists, a spokesman said: “The Prime Minister and Chancellor are fully committed to introducing the health and social care levy in April.
“This is something we have legislated for and we have been clear on the rationale for it.”
He said the money raised would be used to clear the NHS backlog caused by the pandemic, and fund a new social care settlement.
Asked if it was a “no ifs, no buts” commitment, the spokesman said yes.
On the BBC’s Question Time on Thursday defence minister James Heappey said the government was “in listening mode” amid mounting public concern at the imminent tax hike.
He said: “There are plenty of people that are on good salaries that are starting to worry about how they’re going to make ends meet and the government is seeking to address that.
“We’re going to need to do a lot over the next few years to help people with this.”
But the PM’s spokesman said: “We understand that people may not want to pay more in tax, but we’ve set out the rationale for this. It’s clear that the public’s number one priority is to support the NHS.”
Conservative MP Rob Halfon told HuffPost UK he was opposed to the national insurance rise, and called for the money to be raised by “a windfall tax on major industries”.
He said: “We need the money for the NHS - that’s a given. The issue isn’t about whether the money should be spent, but about how you raise it.
“I’m against borrowing because that just puts up taxes in the future. I’m against delaying it because all you do if defer the operation until next year, when we’ll have the same debate all over again.
“The government should definitely raise the money, not through taxes on workers but on millionaires instead, such as a windfall tax on major industries like oil, which is raking in profits at the moment.”