Boris Johnson today risked fueling the Tory mutiny against Partygate and hurt millions of Britons by promising the £12billion National Insurance hike will continue.

In a sharp show of unity after weeks of behind-the-scenes bickering, the prime minister and Rishi Sunak killed hopes the eye-watering raise would be delayed or scrapped.

They insisted in a joint post that the 1.25 percentage point hike to fund NHS and social care reforms is the ‘right plan’ and will continue in April.

But in a nod to the scale of Tory MPs’ anger, Mr Johnson and the Chancellor felt the need to point out that they are instinctively ‘tax-cutting Thatcherites’.

The decision to rule out a U-turn suggests Mr Johnson is feeling more confident in his position as polls show glimmers of a Tory recovery.

There had been allegations that it was ‘vacillating’ and an overhaul could be part of the so-called ‘Operation Save Big Dog’ – the desperate effort to prevent a coup attempt by MPs over breaches of the lockdown of Downing Street and other rows.

Foreign Secretary Liz Truss this morning admitted the tax hike would be ‘unpopular’ – but said the government was in a ‘difficult position’.

In a pointed show of unity after weeks of behind-the-scenes bickering, the Prime Minister and Rishi Sunak (pictured together) killed hopes the eye-watering raise would be delayed or scrapped

The decision to rule out a U-turn suggests Mr Johnson feels more confident in his position as polls show glimmers of a Tory recovery

The latest public finance figures show government borrowing is £13bn lower than expected this year, suggesting Mr Sunak has room to push back the levy.

Mr Johnson and Mr Sunak were forced into the rare step of a joint statement after the Daily Mail and Mail launched calls on Sunday to drop the tax hike.

In their article for the Sunday Times, MM. Johnson and Sunak wrote, “We must move forward with the Health and Social Care Tax.”

The couple said they were ‘Thatcherites’ who believe in ‘sound money’, rather than a ‘magical money tree’.

“We are tax-cutting conservatives. We believe people are the best judges of how their money is spent,” the ministers said.

“We want to get through this phase and continue our agenda, taking advantage of our post-Brexit freedoms to make the UK the business hub of the world.

“We want lighter, better and simpler regulation, especially in new technologies where the UK excels.

“We are Thatcherites, in the sense that we believe in sound money. There is no magic money tree.

But there was an immediate reaction from the Conservatives.

Former Cabinet minister John Redwood called it a huge mistake with people already facing a big hit to their gas and electricity bills in a matter of weeks.

Mr Redwood stressed the tax hike breached a clear Tory manifesto commitment and said the Prime Minister and Chancellor ‘will find the party is extremely angry about this’. But he signaled that the fight against the tax hike would continue, calling on the Prime Minister to “cancel it immediately”.

Senior Tory colleague Robert Halfon said: ‘If they want to raise money for the NHS – which I agree with – we should be taxing millionaires, not millions of workers.

He told BBC Breakfast: ‘All I can do as an MP, a backbench MP, is just urge the government to think again.

He added: “I hope the government will make the cost of living the number one priority.”

The former minister reiterated calls for the government to consider different ways of raising the funds the hike is expected to produce, such as a ‘one-off big business tax’.

Mr Halfon said he was ‘not making any agitation against the Prime Minister’ and would ‘certainly’ not deliver a letter of no confidence to the chairman of the 1922 committee, Sir Graham Brady.

“I just want the government to be the elected government again in 2019 and put first and foremost the reduction in the cost of living and helping struggling families across the country,” he said.

But Ms Truss told the BBC’s Sunday morning programme: ‘We are in a very difficult situation.

“We’ve spent a lot of money on the Covid crisis – which has had public support, whether it’s the furlough scheme, whether it’s the business support scheme, and the reality is we have to pay that money back .”

She added: “Taxes are never popular… they are never popular. As soon as possible, we want to be able to lower our tax rates, we want to stimulate economic growth, because ultimately that is what will make our country successful.

“But we are facing a short-term problem, which is that we have spent significant sums to deal with the Covid crisis which need to be repaid.”

The NI tax hike vow comes as household energy bills are set to rise by almost 50% from April, with industry experts predicting the average annual cost will drop from the current level of £1,277 to £1 £897.

The latest public finance figures show public borrowing is below forecast by £13billion this year, suggesting Mr Sunak has room to push back the levy.

But supporters point out that if it does not happen this year, it will be even more difficult to implement it in the run-up to a general election.

Mike Cherry, national chairman of the Federation of Small Businesses, said: “This regressive tax hike will hit low-income people and struggling community-based small businesses the hardest, leaving less money in people’s pockets to drive our recovery.”

As recently as last week, the Prime Minister reportedly ‘bailed’ over raising taxes in a desperate bid to appease right-wing Tories.

Mr Sunak has insisted that more revenue needs to be raised to fund NHS and social care reforms, although there are allegations that he has privately described the NI move as ‘the tax on the Prime Minister”.

Former Cabinet minister John Redwood called it a huge mistake with people already facing a big hit to their gas and electricity bills in a matter of weeks.

The 1.25 percentage point rise in the NI for both employers and employees was a key factor behind Brexit minister Lord Frost’s shock resignation last month.

Despite Mr Sunak’s personal concerns, the move will be seen as a victory for the Chancellor, who insisted inflation left little room for fiscal easing.

The consumer price index, a measure of inflation, hit 5.4% in December, the highest rate since records began in 1997, according to the Office for National Statistics.

The Chancellor is said to think it would be ‘fiscally irresponsible’ to change course as the result would be more borrowing.

Reports last night said plans to cut VAT on fuel had also been scrapped, which will be interpreted by MPs as a second victory for the Chancellor.