Britain's ambassador to the US Kim Darroch resigned on Wednesday amid an ongoing diplomatic row over leaked emails.
Darroch, a career diplomat, said he wanted to put an end to speculation. "The current situation is making it impossible for me to carry out my role as I would like," he said.
The UK Foreign Office confirmed Darroch's resignation.
Darroch was at the eye of a diplomatic storm after remarks he made about President Donald Trump's administration to the UK officials in confidence, were leaked over the weekend by a local British newspaper.
In those mails, he had called Trump "inept, insecure and incompetent".
Dating from 2017 to the present day, Darroch in the leak emails said: "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."
Distancing himself from the comments made by the UK envoy, Foreign Secretary Jeremy Hunt, who is seeking to become the next Conservative leader and UK's new Prime Minister, said the memos reflected a "personal view", not that of the UK government.
Trump, on the other hand, had responded to the leaked emails and had told reporters, "We're not big fans of that (Darroch) man and he has not served the UK well."
Trump also added, "I can say things about him but I won't bother."
(With inputs from PTI)