Boy, this is looking like a major crisis for UK-US relations. Sir Kim Darroch, UK ambassador to the USA, made confidential comments that Trump was "inept", saying "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."
He doubted if the Trump-led White House "will ever look confident", and policy on issues such as Iran was "incoherent, chaotic".
Well a lot of people suspected all this anyway, but it is the job of diplomats to speak their mind in the knowledge that their comments are for their country's government's eyes only. So the leak of these emails is a serious matter that needs to be investigated. But Trump has reacted in characteristically thin-skinned manner, "we're not big fans of that man and he has not served the UK well", kicking the player rather than the ball.
Trump has said that his administration will no longer deal with Sir Kim, making him "persona non grata", and he has been disinvited to an official dinner.
It looks like May or her successor will have to replace Sir Kim before the end of his term. What a mess.