BORIS Johnson has been urged to explain why he can’t fund social care reforms with the £350 million be promised would be saved every week after Brexit.

The pledge, infamously printed on the side of a Vote Leave campaign bus during the EU referendum campaign, was cited in the Commons as the Prime Minister was grilled on plans to increase National Insurance.

The UK Government is upping the tax by 1.25% to raise £12 billion to help fund England's NHS backlog and social care system – despite warnings that the scheme is inefficient and will hit lower wage workers hardest at a time when “lifeline” Universal Credit benefits are being cut.

Speaking during a Commons debate before the proposals were passed by MPs, Newlands asked Johnson: "The question is why is it necessary at all? This will raise around £12bn a year, but the Prime Minister's Brexit bonus of £350m a week would aggregate to £18bn a year, so where is this money or did it never exist?"

The Prime Minister said the pandemic had "obliged the Treasury to spend £407bn protecting people, their jobs and livelihoods".

He added: "I think people also understand that it is the reasonable and responsible thing to do now to put the NHS back on its feet with the funding it needs and sorting our social care at the same time."

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Meanwhile, Institute for Fiscal Studies chief Paul Johnson said the dual nature of National Insurance contributions meant Johnson's tax hike amounted to double the 1.25% announced.

Speaking to BBC Radio 4's World At One programme, he said: "We keep saying 1.25% - it is really 2.5%.

"It is one-and-a-quarter from the employer on every £100 you earn, it is one-and-a-quarter from the employee - you add that up and it is two-and-a-half per cent.

"It is really a 2.5% tax rise on earnings."

He added: "This is £12bn on top of £25 billion of tax rises in the Budget – this must be the biggest tax rising year in many decades."

The British Chambers of Commerce has also warned there is also a “real danger” the health and social care levy could further stifle the economic bounce-back from the pandemic.

The increase was vehemently opposed by the SNP, who branded it “another Tory poll tax” on Scots.

All six Scottish Tory MPs backed the plans, despite a sizeable backbench revolt among many Conservative parliamentarians.