BORIS Johnson wants to make working Scots fund a tax cut for the richest people in England.

Analysis of the £9.6 billion proposal from the former foreign secretary, who is the favourite to replace Theresa May as Prime Minister (pictured below), revealed it will mostly benefit the wealthy pensioners who make up the Tory membership, and who ultimately vote for the party’s next leader.

Under Johnson’s plans, the 40p tax threshold would jump from £50,000 to £80,000.

His campaign team says the money would be funded in part from the £26.6bn set aside in Treasury for no-deal Brexit preparation, and also from a hike in national insurance contributions.

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That paves the way for a major constitutional crisis.

National insurance contributions are reserved, but income tax is devolved, meaning that Scots would effectively pay for the tax cut.

The SNP called the plan indefensible, while a number of Scottish Tory MPs hit out at the man who could be their next boss.

But Johnson’s team said the Scottish Government should follow his lead.

The SNP MSP Angela Constance said Johnson’s “latest wheeze” was an “appalling insight into the future of the country if he gets his way.”

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She said: “This proposal has more to do with appealing to Tory MPs than to meeting the very real challenges facing the UK. Yet, bizarrely, Boris Johnson remains frontrunner to be the next prime minister.

“Scottish taxpayers now face the prospect of paying for a tax cut for the likes of Boris Johnson and his cronies.

“That would be entirely indefensible – and is only likely to see a further rise in support for independence, which would give Scotland full powers over tax.”

A spokesman for Johnson said: “It’s up to the SNP whether they follow Boris’s leadership or continue with their policy of holding Scotland back as the highest-tax part of the UK. We urge them to follow Boris’s lead.”

Scottish Tory MP John Lamont – who is backing Jeremy Hunt to be the next Tory leader – said the “ill-thought-out plan to hike taxes in Scotland looks more like something Nicola Sturgeon would plan rather than something a Conservative should go near.”

He added: “We need someone who can unite people, not someone whose plans aren’t properly thought through.”

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His colleague from East Renfrewshire, Paul Masterton (pictured above), was more subtle: “Today, and the coming days, will be a good reminder that getting someone to write the right things in your speeches and op-eds about understanding the Union and devolution is one thing, demonstrating it through your policy platform is quite another.”

Scottish Labour MP Ian Murray said Johnson was a “greater threat to the Union than the SNP.”

He added: “When so many people across the UK are suffering in poverty, it is sickening that his priority is massive tax cuts for the wealthiest in society.

“The fact that hard-pressed workers in Scotland would pay towards the tax cuts is a double blow, and will create deep divisions within the Union.

“The Tories are playing fast and loose with the Union and can’t be trusted to protect Scotland’s place in the UK. Ruth Davidson must urgently distance herself from this insulting proposal and explain to Scots what she is planning to do about it when he becomes prime minister.”

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According to economic think-tank IFS, the main beneficiaries of Johnson’s plan will be pensioners on a high income who don’t pay national insurance. They will effectively see their marginal rate of taxation fall from 42% to 20%.

Though pensioners with a big income make up only a small percentage of the country, they make up nearly half of the Tory party’s members, who will ultimately decide who wins the leadership contest and becomes the next prime minister.

In their analysis of the proposal, the Fraser of Allander Institute at Strathclyde University said that the new Fiscal Framework agreed between the Governments in Edinburgh and London meant the Scottish budget “should be protected from any cuts in UK Government spending” resulting from a cut in UK income tax.