The UK government has launched an investigation into who leaked to the media diplomatic memos from the UK ambassador in Washington.

A Foreign Office spokesperson told The Independent a "formal leak investigation will now be initiated" after the Mail on Sunday obtained the highly sensitive documents in which Sir Kim Darroch called the Trump White House “uniquely dysfunctional” and questioned whether it “will ever look competent”.

In one scathing assessment, he wrote: “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.”

The top diplomat also suggested that in order to communicate with the US president “you need to make your points simple, even blunt”.

Although likely to prove highly embarrassing for the government, the Foreign Office defended Sir Kim’s comments as an “honest, unvarnished” assessment of politics in the US.

20 pictures that sum up President Trump's visit Show all 20 1 /20 20 pictures that sum up President Trump's visit 20 pictures that sum up President Trump's visit An awkward greeting As the Queen welcomed Trump to Buckingham Palace, he shared an awkward handshake with her. PA 20 pictures that sum up President Trump's visit "Oi Trump" Essex teenager Ollie Nancarrow mowed this message to Trump in a field near Stansted airport, in order that the president would be forced to see it as he came in to land. BornEco 20 pictures that sum up President Trump's visit A warm welcome Protesters gesture at the helicopter carrying the president as he arrives at Buckingham Palace on the first day of his visit. Getty 20 pictures that sum up President Trump's visit Inspecting the guard After arriving at Buckingham Palace, President Trump inspected an honour guard with Prince Charles. AP 20 pictures that sum up President Trump's visit Khan hits back After the president insulted Sadiq Khan, the London mayor, over Twitter as he landed in Britain, Khan hit back in this video released by Elle. PA 20 pictures that sum up President Trump's visit Mild reception on the Mall The Mall, the road leading to Buckingham Palace, was lacking in pomp as Trump arrived after his visit to Westminster Abbey, only a very small crowd turned out to see the spectacle. Reuters 20 pictures that sum up President Trump's visit Toast with the Queen The president shared a toast with the Queen at the state banquet on his first night in Britain. Reuters 20 pictures that sum up President Trump's visit Creepy kids This picture of Ivanka Trump and husband Jared Kushner, shared to Ivanka's Instagram, was described variously as "terrifying", like "nightmares" and "scarier than the shining." Getty 20 pictures that sum up President Trump's visit Rolling out the red carpet A red carpet was rolled out for the president's arrival to 10 Downing Street. Reuters 20 pictures that sum up President Trump's visit Meeting with May President Trump met with Prime Minister Theresa May on the second day of his visit. They did not speak privately but in a boardroom meeting. Reuters 20 pictures that sum up President Trump's visit Spouses get along First Lady Melania Trump and husband of the prime minister Philip May attended a garden party for the families of Downing Street staff while the two leaders were in their meeting. Getty 20 pictures that sum up President Trump's visit Baby blimp flies again The famous Trump baby blimp made a return in the protests against the president's visit, after first appearing in July last year. EPA 20 pictures that sum up President Trump's visit Crowd gathers A large crowd of protesters gathered in Trafalgar Square in London to protest the president's visit. Notable protesters included a man selling Donald Trump toilet paper and a man dressed as Vladimir Putin controlling a Trump puppet. PA 20 pictures that sum up President Trump's visit Protesters mix and mingle Supporters of the president and protesters of his visit clashed by Parliament Square on the second day of Trump's visit, with some supporters being hit by milkshakes. Reuters 20 pictures that sum up President Trump's visit Toilet Trump A 20ft statue of Trump tweeting while sitting on a golden toilet was placed in Trafalgar Square as protesters gather on the second day of the president's visit. Tom Batchelor / The Independent 20 pictures that sum up President Trump's visit Corbyn speaks In an address to protesters, Labour leader Jeremy Corbyn accused the president of spreading "hatred" and "racism" and expressed disappointment that Sadiq Khan had "been attacked in the way he was." PA 20 pictures that sum up President Trump's visit Churchill hat During his interview with the president on Good Morning Britain, Piers Morgan gave Trump a hat of a style favoured by Winston Churchill, one of Trump's heroes. ITV 20 pictures that sum up President Trump's visit Bus stop baby Activists Special Patrol Group installed this poster in to several bus stops around Portsmouth ahead of the president's arrival for D-Day commemorations PA 20 pictures that sum up President Trump's visit Fly-past with the queen President Trump watched the Red Arrows fly-past with the Queen at an event in Portsmouth to commemorate the 75th anniversary of the D-Day landings AFP/Getty 20 pictures that sum up President Trump's visit Commemoration speech The president gave a speech at an event to commemorate the 75th anniversary of the D-Day landings. Along with Trump, the prime minister and the royal family, French president Emmanuel Macron and 300 Second World War veterans were in attendance. AFP/Getty

“Their views are not necessarily the views of ministers or indeed the government. But we pay them to be candid. Just as the US ambassador here will send back his reading of Westminster politics and personalities,” a spokesperson said.

“Of course we would expect such advice to be handled by ministers and civil servants in the right way, and it’s important that our ambassadors can offer their advice and for it remain confidential.

“Our team in Washington have strong relations with the White House and no doubt ... these will withstand such mischievous behaviour.”

Tom Tugendhat, chair of the Foreign Affairs Committee, had earlier called for a probe and said whoever was responsible for the “very serious breach” should be prosecuted.

The Conservative MP also defended Sir Kim, telling BBC Radio 4’s World at One the job of an ambassador was to “represent the interests and wishes of the British people” and that “diplomats must be able to communicate securely”.

Justice secretary David Guake branded the leaks “disgraceful” and said the ambassador was correct to offer his “unvarnished advice” to government.

Nigel Farage, the Brexit Party leader and friend of Donald Trump, tweeted the leak showed Sir Kim was “totally unsuitable for the job”.

Following Mr Trump’s state visit to the UK in June, Sir Kim warned that although the president had been “dazzled” by the pomp and ceremony of the trip, his administration would remain self-interested and “this is still the land of America First”.

In one of the most recent documents, Sir Kim referred 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.

How President Trump covers up his autocue gaffes

The US and Iran have been at the brink of armed conflict over tensions in the Gulf, and Mr Trump stated that he called off a planned air strike with minutes to spare because of the potentially high number of casualties.

But Sir Kim said that the explanation “doesn't stand up”, and suggested it may have been motivated by Mr Trump’s focus on the 2020 re-election campaign and his previous promises not to involve the US in foreign conflicts.

“It’s more likely that he was never fully on board and that he was worried about how this apparent reversal of his 2016 campaign promises would look come 2020,” Sir Kim said.

He said it was “unlikely that US policy on Iran is going to become more coherent any time soon” as “this is a divided administration”.

In a particularly sensitive leak, a 2017 letter to the National Security Adviser Sir Mark Sedwill – sent 150 days into the Trump administration – laid bare the trouble in the White House.

Media reports of “vicious infighting and chaos” were “mostly true” despite the president’s attempts to brush them off.

Referring to the early allegations of collusion between the Trump campaign and Russia, the memo said “the worst cannot be ruled out”. An investigation by Robert Mueller published earlier this year cleared Mr Trump of collusion, but not of obstruction of justice.