Sir Kim Darroch, the United Kingdom's ambassador to the U.S., resigned Wednesday as his position in Washington became more and more untenable following a Donald Trump freeze-out.

Trump said Monday that he would retaliate against Darroch by ignoring him completely, as punishment for harsh language about him in secret cables leaked to The Mail on Sunday.

By Tuesday he was tweeting that 'wacky' Darroch was 'a very stupid guy' - and that Britain's prime minister Theresa May was 'a disaster.'

Darroch said Wednesday: 'The current situation is making it impossible for me to carry out my role as I would like.'

UK Prime Minister Theresa May called the situation a 'matter of deep regret' after Darroch stepped down: 'The whole cabinet rightly gave its full support to Sir Kim on Tuesday. Sir Kim has given a lifetime of service to the United Kingdom and we owe him an enormous debt of gratitude. Good government depends on public servants being able to give full and frank advice.'

Overnight she tweeted a photo of herself meeting with Cindy McCain, the widow of Trump arch-nemesis Sen. John McCain.

And she told the UK's Parliament in another apparent jab at Trump: 'I hope this House will reflect on the importance of defending our values and principles particularly when they are under pressure.'

Trump ally Boris Johnson, most likely the next prime minister, may have dealt Darroch's career a fatal blow by refusing to say in a televised debate Tuesday that he would keep him on as ambassador.

British Ambassador to the U.S. Sir Kim Darroch, pictured during Donald Trump's recent visit to the United kingdom, has quit his position following the embarrassing leak of his frank and brutal assessments of the American president

In a series of cables, Darroch gave a scathing assessment of the Trump White House, questioning whether it 'will ever look competent'; days later, he has quit

May jabbed at Trump with a photo of herself meeting with Cindy McCain, the widow of Trump arch-nemesis Sen. John McCain

President Trump said Monday that his administration 'will no longer deal with' the UK's ambassador, who trashed him in secret memos leaked to The Mail on Sunday

It is unclear who will replace Darroch and whether May will force through a successor before she leaves or allow her successor - most likely Johnson - to name his own ambassador.

Johnson is believed to have called Sir Kim today to bemoan the fact that he felt he had to resign.

The leak has roiled the British government and exposed deep divisions within the ruling Conservative party's senior ranks.

'IT IS IMPOSSIBLE TO CONTINUE': SIR KIM'S RESIGNATION LETTER In a letter to the head of the Foreign Office, Sir Simon McDonald, Sir Kim said he believed it was 'impossible' for him to carry on in his current role - but said he had been deeply touched by those who had 'offered him support'. In a somewhat emotional response, Sir Simon thanked the life-long civil servant for acting with 'dignity, professionalism and class.' Sir Kim's letter: 'Since the leak of official documents from this embassy there has been a great deal of speculation surrounding my position and the duration of my remaining term as ambassador,' he said. 'I want to put an end to that speculation. The current situation is making it impossible for me to carry out my role as I would like. 'Although my posting is not due to end until the end of this year, I believe in the current circumstances the responsible course is to allow the appointment of a new ambassador. Sir Kim added he was 'grateful' to those in the UK and the US who have offered him support during what he has described as these 'difficult few days'. 'This has brought home to me the depth of friendship and close ties between our two countries. I have been deeply touched'. In his reply to Sir Kim, Sir Simon said he was accepting his resignation with 'deep personal regret'. 'Over the last few difficult days you have behaved as you have always behaved over a long and distinguished career, with dignity, professionalism and class,' he said. 'The Prime Minister, Foreign Secretary and whole of the public service have stood with you: you were the target of a malicious leak; you were simply doing your job. I understand your wish to relieve the pressure on your family and your colleagues at the embassy; I admire the fact that you think more of others than yourself. You demonstrate the essence of the values of British public service.' Advertisement

Johnson is considered favorite to win the election to lead the party, which will then make him prime minister in succession to May.

But he was accused by a junior foreign minister, Alan Duncan, of throwing Sir Kim 'under the bus.'

Showing the anger within his department at the treatment of the diplomat Duncan told the BBC that Johnson had failed to back Darroch during a televised debate late on Tuesday in order to serve his own personal interests.

'He has basically thrown this fantastic diplomat under the bus to serve his own personal interests,' Duncan said.

Foreign Secretary Jeremy Hunt, the other candidate to succeed May, said he was 'deeply saddened' by the diplomat's resignation. Hunt had said he would keep Sir Kim if he became prime minister.

Hunt tweeted: 'Standing up for Britain means standing up for the finest diplomats on the world. It should never have come to this.'

And he said in an official statement that Darroch 'brought dispassionate insight and directness to his reporting to ministers in London.'

Allies of Johnson in turn told MailOnline that Hunt was likely to be fired from the government by Johnson for criticizing Trump.

Nigel Farage, the Brexit Party leader and Trump ally who is the subject of rumors that he could be London's next man in Washington, tweeted that quitting was 'the right decision.'

It is 'time put in a non-Remainer who wants a trade deal with America,' Farage tweeted. He has said he would not want the role, which Trump had publicly touted him for after the 2016 election.

Meanwhile police are trying to investigate the source of the leak, with Hunt saying that they will consider whether it was the result of a Russian hack.

Darroch's withdrawal came in a letter to Sir Simon McDonald, the permanent under secretary at the Foreign and Commonwealth Office, and the highest-ranking career official.

'The current situation is making it impossible for me to carry out my role as I would like,' he wrote. 'I am grateful to all those in the UK and the US, who have offered their support during this difficult few days. This has brought home to me the depth of friendship and close ties between our two countries. I have been deeply touched.

'I am also grateful to all those with whom I have worked over the last four decades, particularly my team here in the US.

'The professionalism and integrity of the British civil service is the envy of the world. I will leave it full of confidence that its values remain in safe hands.'

McDonald responded that he accepted his resignation 'with deep personal regret,' praising him for behaving 'with dignity, professionalism and class.'

'You were the target of a malicious leak; you were simply doing your job,' he wrote.

Trump on Tuesday had eviscerated Darroch on Twitter, calling him '[t]he wacky Ambassador that the U.K. foisted upon the United States.

Darroch 'is not someone we are thrilled with, a very stupid guy,' he wrote. 'I don't know the Ambassador but have been told he is a pompous fool. Tell him the USA now has the best Economy & Military anywhere in the World, by far.'

British Prime Minister Theresa May said in Parliament on Wednesday that Darroch 'has given a lifetime of service to the United Kingdom and we owe him an enormous debt of gratitude; Good government depends on public servants being able to give full and frank advice'

Trump ally Boris Johnson, most likely the next prime minister, may have dealt Darroch's career a fatal blow by refusing to say in a televised debate Tuesday that he would keep him on as ambassador. He campaigned in London pub Wednesday

Nigel Farage, the Brexit Party leader and Trump Ally, agreed with the Darroch resignation and is already being talked up as an outside replacement for him

Trump gave Darroch the back of his hand Tuesday on Twitter as he also lashed out at outgoing Prime Minister Theresa May

Trump's quasi-declaration of statecraft war initially came in a pair of tweets that tore into Britain's outgoing prime minister Theresa May for her handling of Brexit, and suggested that a new leader in London could replace Darroch.

'I have been very critical about the way the U.K. and Prime Minister Theresa May handled Brexit. What a mess she and her representatives have created. I told her how it should be done, but she decided to go another way,' Trump tweeted Monday.

'I do not know the Ambassador, but he is not liked or well thought of within the U.S. We will no longer deal with him,' he added. 'The good news for the wonderful United Kingdom is that they will soon have a new Prime Minister. While I thoroughly enjoyed the magnificent State Visit last month, it was the Queen who I was most impressed with!'

Britain's trade minister said Monday that he would apologize to Ivanka Trump for the leak, in which Darroch described the administration as 'dysfunctional' and 'inept.'

The two met privately on Tuesday.

But Darroch had already been struck from the guest list for a dinner that Treasury Secretary Steven Mnuchin hosted with Trump for the emir of Qatar.

After outgoing prime minister May sat on her hands, it fell to Foreign Secretary Jeremy Hunt to weigh in with a statement calling Trump's comments 'disrespectful and wrong to our Prime Minister and my country.'

The memos annoyed Trump and triggered demands on the British side to find out who had disclosed them.

A Conservative Party member in the UK who has been supportive of the Brexit movement said Tuesday that 'Theresa May has made an absolute mess of Brexit. There is no two ways about that.'

'But everybody knows as well that the ambassador will be following her out the door because people are already talking about who will replace him.'

Trump, the MP said, 'has got it spot on. It's a pity we didn't have him doing the negotiations for us with Brussels.'

Trump first attacked Darroch on Sunday, saying after the bombshell leak that the diplomat had 'not served the UK well.'

Met before: Liam Fox, the trade minister who is groveling to Ivanka Trump, escorted her at the Queen's white tie state banquet for her father's visit to London

In a series of cables, Sir Kim gave a scathing assessment of the White House under the US President, questioning whether it 'will ever look competent'.

On Sunday Trump had unloaded on Sir Kim in return, saying: 'The ambassador has not served the UK well, I can tell you that.

''We are not big fans of that man and he has not served the UK well. So I can understand it, and I can say things about him but I won't bother.'

Trump's aides said Darroch's position was no longer 'tenable' and they expected him to be removed.

His blunt assessments of the Trump administration in briefing notes from 2017 to the present were highly embarrassing for the Foreign Office.

One suggested that in order to communicate with the president 'you need to make your points simple, even blunt.'

He also says: 'We don't really believe this administration is going to become substantially more normal; less dysfunctional; less unpredictable; less faction riven; less diplomatically clumsy and inept.'

Another note questioned whether the White House 'will ever look competent.'

Following Trump's state visit to the UK in June, Darroch warned that although the president had been 'dazzled' by the pomp, his administration would remain self-interested and 'this is still the land of America First.'

Nigel Farage (pictured last week) has called for Sir Kim Darroch to be replaced over his frank assessment of the state of the Trump White House

In one of the most recent documents, Darroch refers to 'incoherent, chaotic' US policy on Iran and questions Mr Trump's publicly stated reason for calling off a retaliatory air strike against Tehran following the downing of an American drone.

Media reports of 'vicious infighting and chaos' were 'mostly true' despite the president's attempts to brush them off, he said.

Referring to allegations of collusion between the Trump campaign and Russia, the memo said 'the worst cannot be ruled out.'

Farage, whom Mr Trump said would do 'a great job' as Britain's ambassador to the U.S., had said Darroch was 'totally unsuitable for the job.'

He added in a tweet that the 'sooner he is gone the better.'

