Donald Trump abandoned the Iran nuclear deal as an act of ‘diplomatic vandalism’ to spite his predecessor Barack Obama, Britain’s Ambassador to Washington wrote in a bombshell memo to Downing Street.

Sir Kim Darroch’s claim – made after Boris Johnson made a doomed trip to the White House to change the President’s mind – is revealed in leaked cables and briefing notes which led to Sir Kim’s resignation last week.

The new revelation comes after an extraordinary row over the freedom of the press blew up this weekend, with Mr Johnson and leadership rival Jeremy Hunt leading the condemnation of Scotland Yard over its threats to prosecute this newspaper.

SCROLL DOWN FOR ISABEL OAKESHOTT'S ACCOUNT OF THE BOMBSHELL REVELATIONS

Britain’s Ambassador to Washington Sir Kim Darroch claimed that Donald Trump abandoned the Iran nuclear deal as an act of ‘diplomatic vandalism’ to spite his predecessor Barack Obama

Who is the officer threatening press with prosecution? Assistant Commissioner Neil Basu He is the Scotland Yard high-flyer with what many regard as the toughest job in policing. Assistant Commissioner Neil Basu, Britain’s top Asian police officer, oversees terrorism investigations at the Metropolitan Police and is the so-called ‘national lead’ officer for counter-terror operations across the UK. Colleagues say he is well-liked within the force and by intelligence officials at MI5 and is likely to be a contender to be the next Met Commissioner. Yet his 27-year police career has not been without controversy, most notably as head of Operations Weeting, Elveden and Tuleta. The three inquiries into phone hacking, computer hacking and alleged payments to police officers by newspapers cost around £19.5 million and were criticised for criminalising journalists. Critics at the time said the Met could have spent the money going after terrorists, murderers and drug dealers. Mr Basu also raised eyebrows when he criticised the Prevent programme – which tries to detect and deradicalise Muslim extremists – as ‘toxic’. ‘Government will not thank me for saying this, but an independent reviewer of Prevent... would be a healthy thing,’ he said. A Hindu, born to an Indian doctor father and a white British mother, he has said he has encountered racism over most of his life. He grew up in Stafford, where he studied at Walton High School before reading economics at Nottingham University. He became a Met police officer in 1992, serving first as a beat bobby in Battersea, South London, then swiftly moving through the ranks as a borough commander in Barnet, North London, and a Commander of South London in 2012. His first major high-profile Met post came in 2014, when he was appointed Commander – Organised Crime and Gangs. Three years later, as a Deputy Assistant Commissioner, Mr Basu was tested as Britain was hit by an unprecedented five terrorist attacks in one year, including the Manchester bombing that killed 22 people and the Westminster attack, which killed four, including a police officer. The most-high profile counter-terrorism investigation overseen by Mr Basu in his current role was the poisoning of Sergei and Yulia Skripal in Salisbury last year, which the Met says was directed by the Kremlin. A father with three sons, Mr Basu is married to Dr Nina Cope, a senior official at the National Crime Agency, often described as Britain’s FBI. Advertisement

Responding to Assistant Commissioner Neil Basu’s incendiary claim that publishing the contents of the documents could be ‘a criminal matter’, Mr Johnson said prosecution ‘would amount to an infringement on press freedom and have a chilling effect on public debate’.

Mr Hunt said that he would ‘defend to the hilt the right of the press to publish those leaks if they receive them and judge them to be in the public interest’.

Health Secretary Matt Hancock goes further today by calling on the police to withdraw Mr Basu’s statement. Writing in this newspaper, he says: ‘The press must be free to publish what it believes to be in the public interest.

Journalists and editors should not be subjected to threats of prosecution or sanction, especially from our own police. Such threats act as a deterrent to journalists doing their jobs – and the ultimate outcome will be an erosion of accountability.’

He was joined by ex-Chancellor George Osborne, who described Mr Basu’s remarks as ‘very stupid and ill-advised’.

In a statement released yesterday, the Met said it had been advised that the publication of the documents could ‘constitute a criminal offence and one that carries no public interest defence’.

In other dramatic developments:

Spies at the Government’s ultra-secretive GCHQ were poised to joined the hunt for the leaker by targeting email and mobile phone records;

The Queen’s former private secretary Christopher Geidt was named by Whitehall sources as a frontrunner to replace Sir Kim in Washington;

Tensions ramped up further between Britain and Iran with the Royal Navy’s £1 billion destroyer HMS Duncan being sent to the Persian Gulf to protect UK vessels against attack by Iranian boats.

Sir Kim’s Iran memo was sent in May 2018, after Mr Johnson – who was then Foreign Secretary – had been dispatched to Washington to make a last ditch plea to President Trump not to abandon the nuclear deal with Iran designed to prevent the regime from building an atomic bomb.

Despite a frantic 26 hours of meetings with Trump’s closest advisers, it became clear that the President was not going to change his mind.

After Mr Johnson returned to London, Sir Kim told No 10 in a ‘diptel’ (diplomatic telegram) that Mr Trump’s Administration was ‘set upon an act of diplomatic vandalism’. The Ambassador wrote that Mr Trump appeared to be abandoning the deal for ‘personality reasons’ because it had been agreed by his predecessor Barack Obama.

Sir Kim suggested there were splits among the President’s closest advisers and said the White House lacked a ‘day-after’ strategy on what to do following withdrawal from the Joint Comprehensive Plan of Action, as the deal was called.

This newspaper’s cache of leaked memos from Sir Kim dominated headlines on both sides of the Atlantic last week, after Trump reacted furiously to Sir Kim describing the White House as a ‘uniquely dysfunctional environment’ and ‘diplomatically clumsy and inept’.

Boris Johnson did not meet President Trump himself on the trip to try and save the Iran nuclear deal that Darroch describes. But he did meet Vice President Mike Pence, pictured. Sir Kim says it was clear the president's advisers had differing opinions

The President called Sir Kim a ‘pompous fool’ and declared that he would no longer deal with him.

Sir Kim resigned on Wednesday shortly after Mr Johnson refused to say during a televised Tory leadership debate whether he would keep the Ambassador in his job if he became Prime Minister.

The leak infuriated the Foreign Office and No 10. Their determination to catch he culprit is indicated by the fact that – according to a Government source – the cyber-experts at GCHQ are about to be brought in to target a shortlist of suspects drawn up by civil service investigators. The spooks have far-reaching powers to intercept communications.

The ambassador suggested that Mr Trump appeared to be abandoning the Iran deal for ‘personality reasons’ because it had been agreed by his predecessor Barack Obama

Sir Kim suggested there were splits among the President’s closest advisers and said the White House lacked a ‘day-after’ strategy on what to do following withdrawal from the deal

The freedom of the press row erupted after Assistant Commissioner Basu said that Scotland Yard was investigating alleged ‘criminal breaches of the Official Secrets Act’ and warned the media that they could be committing an offence by publishing further details. He said: ‘I would advise all owners, editors and publishers of social and mainstream media not to publish leaked government documents that may already be in their possession, or which may be offered to them, and to turn them over to the police or give them back to their rightful owner, Her Majesty’s Government’.

The Met’s Counter Terrorism Command has taken charge of the investigation as it is in charge of any allegations of criminal breaches of the Official Secrets Act.

But Mr Johnson, speaking at a Tory leadership hustings in Bedfordshire, said it could not ‘conceivably be right’ that newspapers ‘publishing such material face prosecution’.

He said: ‘In my view there is no threat to national security implied in the release of this material. It is embarrassing, but it is not a threat to national security. It is the duty of media organisations to bring new and interesting facts into the public domain. That is what they are there for. A prosecution on this basis would amount to an infringement on press freedom and have a chilling effect on public debate.’

Mr Johnson added that he disagreed with former Defence Secretary Michael Fallon – tipped as possible Foreign Secretary under Mr Johnson – for saying that the media should hand back documents to ‘their rightful owner’.

Despite vigorously shaking hands with US Secretary Mike Pompeo and giving a thumbs-up to cameras, Mr Johnson was unable to change the US president's mind

Boris Johnson, pictured with Ivanka Trump on the doomed 2018 trip to persuade Donald Trump not to abandon the Iran deal

Meanwhile, Mr Hunt said: ‘These leaks damaged UK-US relations and cost a loyal Ambassador his job so the person responsible must be held fully to account. But I defend to the hilt the right of the press to publish those leaks if they receive them and judge them to be in the public interest: that is their job’.

Mr Osborne, now editor of the London Evening Standard, told Cressida Dick, the Met Commissioner, that her constabulary was in a mess and she should officially overrule Mr Basu. He said in a tweet: ‘If I were the Metropolitan Police Commissioner, and I wanted to maintain my credibility and the credibility of my force, I would quickly distance myself from this very stupid and ill-advised statement from a junior officer who doesn’t appear to understand much about press freedom.’

Tom Tugendhat, the chairman of the Commons Foreign Affairs Committee, added: ‘I doubt it is a crime to publish. The ability to have a free press is essential.’

Labour Shadow Chancellor John McDonnell said: ‘I don’t welcome the Met Police stepping in to threaten legal action against broadcasters and newspapers. If someone has committed any crime under the Official Secrets Act – individual civil servants – of course the police will investigate.’

The Met’s Counter Terrorism Command has taken charge of the investigation as it is in charge of any allegations of criminal breaches of the Official Secrets Act

And Liberal Democrat leadership contender Ed Davey said: ‘Press freedom has never been so under attack in my lifetime. There are alarming signs of a creeping police state tearing down the ancient democratic pillar of a free press, which is essential to hold government to account.

‘The Leader of the Opposition attacks the BBC for daring to point out his party’s anti-Semitism and the incoming Prime Minister threatens to close down Parliament, all of which adds up to an attack on our very democracy. Threatening journalists with the spectre of jail for bravely reporting the story is a disgrace.’

In response to the growing furore, Mr Basu released a further statement yesterday in which he said that the police ‘respect the rights of the media and has no intention of seeking to prevent editors from publishing stories in the public interest in a liberal democracy.

'The media hold an important role in scrutinising the actions of the State’. However, he stoked suspicions that the force had come under political pressure by adding: ‘We have received legal advice that has caused us to start a criminal enquiry into the leak of these specific documents as a potential breach of the Official Secrets Act. The focus of the investigation is clearly on identifying who was responsible for the leak.

‘However, we have also been told the publication of these specific documents, now knowing they may be a breach of the Act, could also constitute a criminal offence and one that carries no public interest defence. We know these documents and potentially others remain in circulation. We have a duty to prevent as well as detect crime and the previous statement was intended to alert [newspapers] to the risk of breaching the Act’.

Following the furore over the Washington cables, Lord Geidt, who spent ten years as the Queen’s private secretary, is being tipped as a potential replacement for Sir Kim because his impeccable royal connections would impress Trump – and he has made it clear that he is ‘looking for new challenges’.

A Foreign Office spokesman said: ‘A police inquiry into the totally unacceptable leak of this sensitive material has begun. The perpetrator should face the consequences of their actions. It’s not news that the US and UK differ in how to ensure Iran is never able to acquire a nuclear weapon; but this does underline that we do not shy away from talking about our differences and working together.

‘That is true of the current tensions in the Gulf where we, the UK, are in close contact with our American and European allies to de-escalate the situation.’

Trump ‘is set upon an act of diplomatic vandalism’: Sir Kim Darroch's cables describe how Boris failed to save Iran deal, claim the President was against it for 'personality reasons' and suggest splits among White House advisors

BY ISABEL OAKESHOTT FOR THE MAIL ON SUNDAY

Standing in front of Corinthian columns at the US Department of State, Boris Johnson vigorously pumped the hand of his American counterpart Mike Pompeo and gave a thumbs-up to reporters.

But as the Foreign Secretary turned on his heels after the photocall, he knew that his hastily arranged diplomatic mission to Washington was on the brink of failure.

It was May 7, 2018, and Mr Johnson had been hurriedly dispatched to make a last-ditch plea to President Donald Trump not to abandon a nuclear deal with Iran, regarded by many experts as critical to prevent the regime from building an atomic bomb.

During a frantic 26 hours of meetings, Mr Johnson met all the key ‘Trump Whisperers’ – those advisers with the ear of America’s unpredictable leader. It became clear, however, that despite the ‘special relationship’ between Britain and the US, Mr Johnson was not going to change the President’s mind.

During a frantic 26 hours of meetings, Boris Johnson met all the key 'Trump Whisperers' but despite vigorously shaking hands with US Secretary Mike Pompeo and giving a thumbs-up to cameras, he was unable to change the US president's mind

In an explosive diplomatic cable sent to London hours after Mr Johnson returned home, Sir Kim Darroch, Britain’s Ambassador to the US, lamented that Mr Trump’s Administration ‘is set upon an act of diplomatic vandalism’.

In a blunt assessment, Sir Kim wrote that Mr Trump appeared to be abandoning the Iran nuclear deal for ‘personality reasons’ –because it had been agreed by his predecessor Barack Obama.

And Sir Kim suggested there were splits among the President’s closest advisers and claimed the White House lacked a ‘day-after’ strategy on what to do after withdrawing from the Joint Comprehensive Plan of Action (JCPOA), the official name for the Iran deal.

The new telegram is disclosed today, a week after this newspaper first revealed an astonishing cache of leaked memos from Sir Kim.

Our revelations, which have dominated headlines on both sides of the Atlantic, infuriated the President and prompted him to brand Sir Kim a ‘pompous fool’ and ‘wacky’ and declare on Twitter that he would no longer deal with him.

In a blunt assessment, Sir Kim wrote that Mr Trump appeared to be abandoning the Iran nuclear deal for ‘personality reasons’

Sir Kim resigned on Wednesday after Mr Johnson refused to say during a televised Tory leadership debate whether he would keep the Ambassador in his job if he became Prime Minister. Appearing alongside leadership rival Jeremy Hunt, Mr Johnson expressed only mild criticism of Trump’s comments and refused to back the highly experienced diplomat.

His cold shouldering of Sir Kim was in stark contrast to their joint efforts 14 months earlier to try to convince the White House not to junk the Iran nuclear deal.

Signed in July 2015 by Iran and six major powers, including the US and Britain, the deal limited Iran’s nuclear programme in return for the lifting of crippling sanctions.

Under the accord, Iran promised to slash its uranium stockpile by 98 per cent for 15 years, dramatically reduce its number of centrifuges which can be used to enrich uranium, and allow forensic inspections of its nuclear facilities.

According to the Obama Administration, which viewed it as a major diplomatic triumph, the deal would increase the so-called ‘break-out time’ – the time it would take Iran to produce enough highly enriched uranium to build a nuclear bomb – from a couple of months to a year or more.

But Mr Trump hated the pact, which he branded a ‘disaster’ and ‘the worst deal ever negotiated’ during his 2016 election campaign.

To the dismay of his future allies in Europe, he declared before the election that his ‘number one priority’ would be to ‘dismantle the disastrous deal with Iran’. It was perhaps, therefore, unsurprising that Mr Johnson was in an uncharacteristically sober mood as he settled into his eight-hour flight to Washington DC almost two years later on May 6, 2018.

Sir Kim had done a good job of organising what he would later describe in his diplomatic telegram as ‘a packed programme’ for the Foreign Secretary.

During his short visit, Mr Johnson would see Mr Trump’s National Security Adviser, John Bolton, and his Chief of Staff John Kelly, as well as Trump’s daughter Ivanka, and her husband Jared Kushner, who was heavily involved in the Middle East peace process.

By a stroke of luck, there would also be an opportunity to meet Mr Pompeo, Mr Trump’s newly appointed Secretary of State, whose planned trip to North Korea had been delayed.

But disappointingly, Mr Johnson would not be seeing the President himself. Everything had happened too fast and he would have to make do with meeting Vice President Mike Pence, even if this would make him the first UK Minister to secure face-time with Trump’s deputy.

In a canny move, however, Johnson appeared on Fox and Friends – Mr Trump’s favoured TV news show – and made an impassioned and direct appeal for the President to change course.

‘What if the Iranians do rush for a nuclear weapon?,’ he asked. ‘Are we seriously saying that we’re going to bomb those facilities? Is that really a realistic possibility or do we work with what we’ve got and push back on Iran together?’

In his memo, Sir Kim details how, during his crunch meetings with Trump’s inner circle, Mr Johnson lavished praise on the Americans for their work in North Korea; thanked them for their support over Russia’s poisoning of Sergei and Yulia Skripal in Salisbury; and acknowledged the ‘impeccable cooperation’ between the US and the UK over recent air strikes in Syria.

Such flattery came easily to the Old Etonian. The main subject on the agenda – Iran – would be much more tricky.

In the two-page summary, written by Sir Kim to Mr Johnson and sent to the Foreign Office, No 10, the Ministry of Defence and elsewhere in Whitehall, the Ambassador revealed how the Foreign Secretary said he ‘recognised the flaws and inadequacies in the deal’ but argued the White House should stick with it. Paraphrasing Mr Johnson’s argument, he wrote: ‘A deal which established a break-out period of more than a year, took away two-thirds of Iran’s centrifuges, reduced their enriched uranium stockpiles by 95 per cent, concreted over the heavy water reactor [potentially used to produce plutonium that could be used in a bomb] and included an exceptionally rigorous inspection regime, should not be thrown away.’

Vice President Pence, Mr Bolton and Mr Pompeo listened respectfully – with the latter showing signs that he disagreed with Mr Trump’s position, according to the cable.

During their meeting on the seventh floor of the Department of State, Mr Pompeo ‘did some subtle distancing by talking throughout about “the President’s decision” ’ and hinted that he had tried – and failed – to ‘sell’ a revised text to Trump, according to Sir Kim’s memo.

He also hinted to Mr Johnson that he was hoping to persuade the President to soften the impact of axing the deal by, for example, holding off imposing so-called secondary sanctions designed to punish other countries for doing business with Iran. After their talks, Mr Johnson and Mr Pompeo briefly appeared before reporters in the Department’s Treaty Room Suite, shaking hands and exchanging stilted pleasantries.

‘Absolutely wonderful to see you,’ gushed the Foreign Secretary. ‘Thank you for making the time.’

‘These are important times, so thank you very much for being here,’ replied Mr Pompeo, who did not answer a reporter who asked whether he had been ‘persuaded’ by Mr Johnson.

Vice President Pence, Mr Bolton and Mr Pompeo listened respectfully – with the latter showing signs that he disagreed with Mr Trump’s position

But Vice President Pence had a blunter message during his meeting with the Foreign Secretary in the White House.

Sir Kim’s report details how he told Mr Johnson that Mr Trump’s ‘clear inclination’ was ‘to start again rather than build on faulty foundations: he wanted a much tougher deal.’

Sir Kim added in his memo to Johnson: ‘Pence also took you aside and hinted that the President was looking for a new deal which “covered everything”: stopping Iranian nuclear activity – enrichment, production, reprocessing – entirely; halting their ballistic missile development; and forcing them to back off from their activities in the region.’

In the interests of diplomacy, Mr Pence reassured Mr Johnson that the White House would want to stay close to its allies and consult the British about next steps.

‘This is not about walking away, it’s about walking to something better,’ the Vice President reportedly said.

However, Sir Kim described how the British delegation was surprised by the inability of any of Mr Trump’s advisers to explain why he was so determined to junk the deal or their strategy after withdrawing from it.

Darroch said Mr Trump's decision to withdraw from the deal was 'the end of a long road' and highlighted how National Security Adviser John Bolton's arrival in the White House in April 2018 'was widely predicted to cement this outcome'

‘None of the three could articulate why the President was determined to withdraw, beyond his campaign promises,’ he wrote. ‘And, even when you pressed, none had anything much to say about the day after, or a Plan B, beyond reimposition of US sanctions.’

Such damning criticism echoed another memo, revealed by this newspaper last week, in which Sir Kim described the White House as a ‘uniquely dysfunctional environment’ and ‘diplomatically clumsy and inept’.

The one crumb of comfort for Mr Johnson was that the ultra-hawkish Mr Bolton, who has previously called for the bombing of the Iranian regime, ‘said explicitly that he [Trump] wasn’t favouring a military option’.

At the end of a gruelling series of meetings, the Foreign Secretary left Washington empty-handed.

However, Sir Kim described how the British delegation was surprised by the inability of any of Mr Trump’s advisers to explain why he was so determined to junk the deal or their strategy after withdrawing from it

Sir Kim could not hide his disappointment when at 1.38pm in Washington on May 8, he sent his cable.

‘I’m grateful to you for coming out on short notice and undertaking such a packed programme,’ he told Mr Johnson. ‘The outcome illustrated the paradox of this White House: you got exceptional access, seeing everyone short of the President; but on the substance, the Administration is set upon an act of diplomatic vandalism, seemingly for ideological and personality reasons – it was Obama’s deal.

‘Moreover, they can’t articulate any “day-after” strategy; and contacts with State Department this morning suggest no sort of plan for reaching out to partners and allies, whether in Europe or the region.’

Less than two hours later, the failure of Mr Johnson’s mission was confirmed when Mr Trump announced he was terminating America’s participation in the Iran deal and re-imposing sanctions.

In a second cable sent at 6.58pm Washington time, Sir Kim reported that ‘following a typically hyperbolic statement on the nature of the “murderous” Iranian regime, Mr Trump signed a presidential memorandum to start the process of reinstating US nuclear sanctions.’

Mr Trump’s decision was, he said, ‘the end of a long road’ and highlighted how Mr Bolton’s arrival in the White House in April 2018 ‘was widely predicted to cement this outcome.’

‘Much of the speech echoed lines we have heard from Bolton in person,’ he explained.

Before signing off for the night he reassured London that British diplomats had pulled out all the stops. It was clear, however, that the special relationship had its limits.

‘We did everything we could across government to save the deal. Many said it would go on the first day of Trump’s time in office. There has been no stone unturned in our attempt to persuade and shape the Administration’s view,’ he sighed.

The same frustration was evident the following day when Mr Johnson made a statement to the House of Commons about the President’s decision.

‘The Government regret the decision of the United States Administration to withdraw from the deal and reimpose American sanctions on Iran,’ he told MPs.

‘We did our utmost to prevent this outcome: from the moment that President Trump’s Administration took office, we made the case for keeping the JCPOA at every level.’

Choosing his words carefully, he also appeared to acknowledge Sir Kim’s concerns at the White House’s lack of a ‘day-after’ strategy. ‘Now that our efforts on this side of the Atlantic have not succeeded, it falls to the US Administration to spell out their view of the way ahead.’

For Mr Johnson, however, the visit had not been completely in vain.

Two months later and despite his criticism of Mr Trump’s withdrawal from the nuclear deal, the President used a visit to the UK to hailed the Foreign Secretary as ‘a very talented guy’ who ‘would be a great Prime Minister’.

Now, with critics accusing him of throwing Sir Kim ‘under the bus’ to protect his leadership ambitions, Mr Johnson may have cause to regret receiving such a fulsome endorsement.

Trump blew his top and Donald Jr was 'furious': How the world reacted to explosive cables and Sir Kim Darroch realised his 'time was up' after the President refused to work with him and Boris Johnson failed to back him

The first small tremors were felt in Whitehall nine days ago, when The Mail on Sunday contacted the Foreign Office to say that we were in possession of Sir Kim Darroch's dynamite memos.

At first, Foreign Secretary Jeremy Hunt's officials reacted with misplaced sang froid. 'Our team in Washington have strong relations with the White House and we have no doubt that these will withstand such mischievous behaviour,' a spokesman said coolly.

That assessment is likely to prove accurate about Britain's long-term close relationship with the US – but not for the unfortunate Sir Kim.

Shortly after an Oval Office briefing, President Trump launched his first Twitter tirade on Sir Kim: 'I do not know the Ambassador, but he is not liked or well thought of within the US,' he wrote. 'We will no longer deal with him'

Despite their unruffled public stance, the Foreign Office immediately contacted Downing Street and Mrs May, who was in her Maidenhead constituency, was soon made aware of the situation. It was agreed that No 10 should circle the wagons around Sir Kim, because it was his job to provide an 'honest, unvarnished' assessment of the situation in America.

Media all over the world reported the Ambassador's unguarded comments, which gave a rare insight into the workings of the Trump Administration. All eyes were now on the reaction from the White House.

With Washington empty for the Fourth of July weekend, President Trump was staying with his family at his 600-acre Bedminster resort in New Jersey.

There, as his most senior allies gathered inside the Trump National Golf Club's vast Georgian revival clubhouse, they circulated the story between them on WhatsApp within minutes of it first appearing on MailOnline. Mr Trump's son, Don Jnr, reacted 'furiously' to the story, a Washington source said.

The first sign of trouble came when Arthur Schwartz, a long time 'fixer' for Don Jnr broke cover to tweet his disgust with Sir Kim. At the same time Raheem Kassam, a former aide of Nigel Farage who is now a Washington-based Trump activist, was flagging up the story online.

The President was first made aware of the row early on Sunday; his first public mention came during a short 'huddle' with journalists as he boarded Air Force One at Morristown airport on his way back to Washington later that day. 'The Ambassador has not served the UK well, I can tell you that... And I can say things about him, but I won't bother,' he said.

His promise to stay quiet did not survive a visit to the White House by State Department officials on Monday morning, where they briefed Mr Trump in full on The Mail on Sunday's revelations.

Back in London, Mrs May had ordered supportive messages to be sent to Sir Kim, assuring him that his job was safe: her time in No 10 has been bedevilled by leaks, and she was determined that the culprit should not claim a 'scalp'.

Mr Trump's son, Don Jnr, reacted 'furiously' to the story, minutes after it was published on the Mail Online

At the same time, officials at the UK Embassy in Washington were insisting to the White House that Sir Kim had said 'lots of positive things about the President too'.

However, our diplomatic efforts were being undermined by hardliners in Trump's Administration who were urging him to 'go nuclear' against Sir Kim. Shortly after his Oval Office briefing, Trump launched his first Twitter tirade: 'I do not know the Ambassador, but he is not liked or well thought of within the US,' he wrote. 'We will no longer deal with him.'

The storm grew when Sir Kim was disinvited to a White House dinner that evening, with the President returning to Twitter early on Tuesday morning: 'The wacky Ambassador that the UK foisted upon the United States is not someone we are thrilled with, a very stupid guy,' he wrote,

By Tuesday afternoon, beleaguered Sir Kim was still emailing friends in London valiantly insisting he would 'be fine'.

Boris Johnson insisted that his refusal to endorse Sir Kim during his televised debate with Jeremy Hunt had been misinterpreted

But others in Whitehall were not so sure. One senior Minister told The Mail on Sunday: 'If Sir Kim had been half as plugged into Washington as he claims, then he would have known the way the wind was blowing and resigned on Sunday morning. His arrogance that he could tough it out in the face of the inevitable Trump storm was ill-conceived.'

Wednesday morning – the day of Sir Kim's resignation – dawned with Downing Street still expecting him to stay in his post: at No 10's critical 8.30am meeting, no mention was made of his resignation. But by mid-morning London time, Sir Kim had concluded that his position was untenable: Mrs May had just enough time to prepare a statement to deliver at noon at Prime Minister's Questions, just after the news had broken.

One senior Minister told The Mail on Sunday: 'If Sir Kim had been half as plugged into Washington as he claims, then he would have known the way the wind was blowing and resigned on Sunday morning.'

At the time, Boris Johnson was being interviewed in a London pub as part of his leadership campaign. He returned to one of his two campaign headquarters, where he received a text from Sir Kim. A 15-minute conversation followed, during which Mr Johnson paid tribute to the outgoing Ambassador for his decades of public service.

Mr Johnson insisted that his refusal to endorse him during his televised debate with Mr Hunt the previous evening had been misinterpreted and said he had been evasive as he did not want to 'politicise the Civil Service'. Members of Mr Johnson's campaign blame Jeremy Hunt's team for 'whipping up' the anger for political gain.

Sir Kim is understood to have told Mr Johnson that he had realised that his 'time was up' when Trump announced that he would no longer do business with him; that view was reinforced when he watched a recording of the debate and realised how political the issue had become.

But relations have been strained between Mr Johnson and Sir Kim for some time, dating back to a visit Mr Johnson made to Washington two years ago as Foreign Secretary.

Assistant Commissioner Neil Basu made an extraordinary plea on Friday for the leaker to 'turn themselves in'

An official who was then – but not now – working for Boris broke into the British Embassy at 2am after a long drinking session: he climbed over the wall and into his bedroom, where he was violently sick, to the horror of Sir Kim and his team.

The relationship has also been soured by the leak of another diplomatic memo by Sir Kim in 2016 which revealed his unflattering views of the Trump Administration – a leak which Foreign Office officials believed, without providing any evidence, originated from within Mr Johnson's then team.

Sir Kim's resignation on Wednesday enraged civil servants and diplomats across Whitehall, leading to the investigation into the current leak being ramped up.

By Thursday morning, more than 320 people had been contacted about the breach, and a shortlist of four suspects had been drawn up.

But as Assistant Commissioner Neil Basu was making his extraordinary plea on Friday for the leaker to 'turn themselves in' – while claiming that publishing the leaks could be 'a criminal matter' – Government sources were already admitting that the cyber-spies at the Government's GCHQ were likely to be brought in to step up the hunt for the culprit.

And despite the speed at which the President's public fury had erupted, by Friday Mr Trump was mending fences, saying he wished Sir Kim well.

He admitted that the US had leaking problems that he needed to fix as well, and insisted that Sir Kim had 'actually said very good things about me'.

Diplomats in Washington and officials in London breathed a sigh of relief as the storm appeared to be passing after just five days.

Whitehall officials believe it was a personal dislike of Sir Kim's comments that prompted Trump's reaction from the White House, rather than a wider threat to the special relationship, and expect a marked improvement in relations if Mr Johnson becomes Prime Minister.