BORIS Johnson seemed to accidentally announce plans for a major Tory tax cut yesterday.

The Prime Minister was speaking to workers at a fabrication yard in Teesside when he said he was looking to hike the threshold at which people start paying National Insurance.

The supposed slip up stunned party minders, though there was some speculation it helped overshadow the row about the Tory party Twitter account pretending to be a fact-checking service during Tuesday night’s live televised debate.

As he took questions, industrial chemist Claire Cartlidge, asked Johnson: “Do you mean low tax for people like you or low tax for people like us.”

Johnson replied with detail that was not meant to be unveiled until the Tory party manifesto launch.

The National: Boris Johnson

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He said: “I mean low tax for people of the working people.”

“If you look at what we’re doing and what I’ve said in the last few days, we’re going to be cutting national insurance up to £12,000, we’re going to be making sure that we cut business rates for small businesses, we are cutting tax for working people.”

The policy would effectively be a tax cut of more than £400 for everyone earning more than the current threshold of £8632.

Though the party very quickly clarified Johnson’s remarks saying the threshold would rise to £9500 next year then lift it gradually over many years until it reached £12,000.

The Resolution Foundation said raising the threshold to £12,500 would give most workers a tax cut of £480, at a cost of about £11 billion to the Treasury.

Labour’s shadow chancellor John McDonnell said the tax cut didn’t go far enough: “Even after ten years of cruel cuts and despite creaking public services the Tories still think the answer to the challenges of our time is a tax cut of £1.64 a week, with those on Universal Credit getting about 60p.

“Meanwhile independent experts have said this will cost up to £11bn so everyone who relies on public services and social security will be wondering whether they will be paying the price.

“The Tories are stuck in the 1980s while a Labour Government will tackle head-on the climate and human emergencies of our time.”

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Another worker at the factory asked the Prime Minister why he would not publish the controversial report by the Intelligence and Security Committee on Russian interference in the EU referendum.

Johnson said: “There’s absolutely no evidence that I’ve ever seen of any Russian interference in UK democratic processes.”

He added: “And as for that particular report I saw no reason whatever to change to timetable for publication just because there was a General Election going on.”

Jeremy Corbyn is set to launch Labour’s manifesto today with an attack on the “rich and powerful”.

The veteran left-winger will say the party’s manifesto is “fully costed, with no tax increases for 95% of taxpayers.”

He is due to tell supporters: “Over the next three weeks, the most powerful people in Britain and their supporters are going to tell you that everything in this manifesto is impossible.”

Corbyn will add: “If the bankers, billionaires and the establishment thought we represented politics as usual, that we could be bought off, that nothing was really going to change, they wouldn’t attack us so ferociously. Why bother?”