Donald Trump has waded into the General Election campaign, praising Boris Johnson and dismissing out of hand the big fear of Labour, the SNP and the Liberal Democrats that he wants US companies to buy up Britain’s NHS following Brexit.

The US President, in London for the 70th anniversary meeting of Nato, insisted he would "stay out" of the election campaign because he did not want to "complicate it". Yet he went on to declare himself a “fan of Brexit” and told reporters openly: “Boris is very capable and he'll do a good job."

Asked if he could work with Jeremy Corbyn as Prime Minister, Mr Trump replied: “I can work with anybody. I'm a very easy person to work with."

When quizzed about the prospect of American companies snapping up parts of the NHS in a post-Brexit trade deal, the President was adamant that the US was not interested in it, insisting: “We wouldn't want to if you handed it to us on a silver platter. We want nothing to do with it.”

Mr Corbyn, who held a press conference last week to reveal unredacted documents, which he claimed proved the NHS would be “on the table” in any post-Brexit UK-US trade talks, said he was "pleased" about Mr Trump’s comments but asked: "If that's the case, why have these talks gone on for two years? Why have they been kept secret?"

Jo Swinson, the Liberal Democrat leader, insisted the President could not be trusted while her colleague Chuka Umunna insisted the public would “rightly take these comments with a lorry load of salt”.

But on the campaign trail in Salisbury, Boris Johnson again brushed aside talk of selling off parts of the NHS to the Americans, saying he could "categorically rule out any part of the NHS will be on the table in any trade negotiations", adding this included pharmaceuticals.

"This is pure Loch Ness Monster, Bermuda Triangle stuff," declared the Prime Minister.

Mr Corbyn stressed that if he met Mr Trump at the Buckingham Palace reception to mark the Nato anniversary yesterday evening he would tell him: "I hope you'll understand how precious our National Health Service is and in any future trade relationship with the USA none of our public services are on the table, none of our public services are for sale."

But The Herald was told there was “no opportunity” for Mr Corbyn to raise his concerns about US companies wanting to buy parts of the NHS face to face with the President.

Last night, hundreds of demonstrators, including NHS workers, gathered outside Buckingham Palace under the banner of “Trump, hands off our NHS” as police helicopters hovered overhead.

Earlier, the Labour dismissed as “utter nonsense” questions raised over whether Russian disinformation was behind the release of the 451-page unredacted report on UK-US trade talks.

Today, Downing St and Tory HQ will wait nervously to see if the President wades deeper into British domestic politics as he is due to hold a press conference following the Nato summit in Watford when he is bound to be asked questions about election issues.

Party chiefs are also keeping a wary eye on Mr Trump’s Twitter-feed.

Normally, Mr Johnson would have had a one-to-one bilateral with the President and even a joint press conference. But Conservative chiefs want to keep Mr Trump at arm’s length from the campaign fray, acknowledging that any direct intervention could be unhelpful to the governing party’s campaign. Labour accused the PM of “running scared”.

As Labour HQ becomes jittery about talk of traditional supporters moving over to the pro-Brexit Conservatives in its strongholds across northern England and the Midlands, Emily Thornberry, a pro-Remain member of the Shadow Cabinet, insisted Labour could still close the gap on the Tories.

Denouncing the Lib Dems’ proposal to revoke Article 50 if they won power, the Shadow Foreign Secretary said: "You can't just go back on a decision in a referendum. But if after the public have seen what leaving really looks like versus Remain, it may well be that confirmatory referendum can be won by Remainers.”

She insisted a confirmatory referendum would be the “final word” and added: “But in the end, after the paralysis caused by a Conservative government unable to agree amongst itself what it wants to do, this is the way forward."

But a Kantar poll gave the Tories a 12-point lead, placing them on 44 per cent, up one on a week ago, with Labour unchanged on 32 points, the Lib Dems up one on 15 and the Brexit Party down one on just two.

In London, Mr Corbyn’s party is faring better. A YouGov poll gave Labour a 17-point lead over the Tories, placing it on 47 per cent, up eight on November; yet still below the 54 points Labour achieved in 2017. With the Tories up a point on 30, it is the Lib Dems who are being squeezed on 15 points, down four in a month; yet this is still way above the nine points they achieved two years ago.

Tory strategists believe President Trump’s visit and Friday’s final televised head-to-head leaders’ debate on BBC1 are Mr Corbyn’s last chance to change the dynamic of the campaign.

One senior Conservative figure noted: “The debate is the last make-or-break moment for Corbyn.”

Meanwhile, the chances of the BBC’s Andrew Neil securing a live interview with Mr Johnson look doomed. The broadcaster tweeted last night: “There are not really any negotiations going on. We’re simply waiting on a date, time and venue. As we have for several weeks. So far - not a sausage.”

It is thought, given the hard time the Scot gave Mr Corbyn, Tory high command is calculating the hit the party’s campaign from the PM avoiding Mr Neil’s interrogation would be far less than the fall-out from a car crash interview.

In other developments -

*Grant Shapps, the Transport Secretary, announced that a Conservative majority government would boost local trains, buses and trams in England's biggest cities - and the towns around them - with £4.2 billion of new spending, which would produce a knock-on windfall for the Scottish Government of almost £400m. Labour dismissed the move, saying it was a “pathetic attempt to cover up the Government’s disastrous and incompetent failure to invest in public transport”.

*John McDonnell, the Shadow Chancellor, in a campaign speech in Birmingham, will pledge that Labour would “end rip-off Britain with a Government that is on your side,” saying that a future Corbyn administration’s plan for real change could save families more than £6,700 a year.

*the Liberal Democrats pledged their commitment to transform mental health services in the UK by creating a binding Student Mental Health Charter, which would require all universities to guarantee access to high quality mental health services for their students.

*the Green Party said it would invest £12 billion a year in renewables to “revolutionise” the way the country produced energy, which would see the building of an extra 40,000 wind turbines by 2030 and the creation of 75,000 jobs.

*Mr Corbyn, after four times refusing to apologise for Labour’s handling of the anti-Semitism row during last week’s Andrew Neil interview on the BBC, told ITV’s This Morning: he was "very sorry" for "everything that has happened".

*Lord Patten, the former Conservative Chairman, claimed Mr Johnson and Mr Trump shared a “certain, rather elastic relationship with the truth”.

*Weather forecasters are warning of a cold snap with up to 11 inches of snow next week when voters go to the polls.