US President Donald Trump has launched a blistering attack on the departing British Prime Minister and the UK ambassador to Washington after memos surfaced in which the envoy called him incompetent, inept and insecure. In a series of tweets he said his government will "no longer deal" with UK Ambassador Kim Darroch. The fallout from his comments were swiftly felt as US Treasury Secretary Steven Mnuchin disinvited Mr Darroch from a dinner with the Emir of Qatar on Monday evening. Mr Trump is hosting Sheikh Tamim Bin Hamad Al Thani and is due to meet him on Tuesday. He is also expected to be frozen out of a meeting with Mr Trump's daughter Ivanka, who is due to meet the British trade secretary Liam Fox on Tuesday. In a cut-throat comeback to the leaked memo fiasco, Mr Trump also criticised Theresa May for her Brexit blunders. “I have been very critical about the way the UK and Prime Minister Theresa May handled Brexit,” he said. “What a mess she and her representatives have created. I told her how it should be done but she decided to go another way. “I do not know the ambassador, but he is not liked or well thought of within the US. We will no longer deal with him. “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.” The president's comments came after secret diplomatic memos from Mr Darroch, UK ambassador to the US, were leaked by <em>The Mail on Sunday.</em> The memos<em> </em>said the Trump administration was marked by "vicious infighting and chaos" before questioning whether it "will ever look competent". “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,” Sir Kim wrote. He said the administration had become “uniquely dysfunctional” under Mr Trump. Mr Darroch said the American policy on Tehran was “incoherent and chaotic”, and he challenged the president’s publicly stated reason for calling off air strikes on Iran after it shot down a US drone. Tension has been high between EU states and America on Iran, as Washington threatened more sanctions and European leaders hesitated to impose penalties, urging Tehran to keep to the 2015 nuclear deal from which America pulled out last year. The British Foreign Office did not dispute the veracity of the memos, with a spokesman saying “we pay them [ambassadors] to be candid”. “Our team in Washington have strong relations with the White House and no doubt these will withstand such mischievous behaviour,” the spokesman said. On Sunday night, the US president hit back, saying Mr Darroch, “has not served the UK well”, while White House aides called for the ambassador to be fired. Earlier on Sunday, the British government announced that a formal inquiry would be held into the leaking of the memos. “We have made clear to the US how unfortunate this leak is,” a Downing Street spokesman said on Monday, after Mr Trump’s response. “The selective extracts leaked do not reflect the closeness of and the esteem in which we hold the relationship.” The spokesman said that the UK government continued to support Mr Darroch. “The UK has a special and enduring relationship with the US based on our long history and commitment to shared values, and that will continue to be the case,” he said. Mr Trump’s criticism of Mrs May comes at a time when power is about to change hands in the UK, as the country searches for a new prime minister. Jeremy Hunt, the British Foreign Secretary, and Boris Johnson, the former foreign secretary and mayor of London, are the two candidates vying to enter Downing Street. Mr Trump has said he wants Mr Johnson to become the next prime minister.