US President Donald Trump has criticised the UK ambassador who said in leaked emails that his administration was "inept".
Mr Trump said: "The ambassador has not served the UK well, I can tell you that."
Emails from Sir Kim Darroch said Mr Trump's White House was "uniquely dysfunctional" and "divided".
Trade secretary Liam Fox said the leak was "unprofessional, unethical and unpatriotic", the BBC reported.
He said that whoever released the emails had "maliciously" undermined the defence and security relationship with the US, "the most important global relationship that we have".
"I hope if we can identify the individual, either the full force of internal discipline - or if necessary the law - will be brought to bear because this sort of behaviour has no place in public life," he said.
As the Foreign Office launched an investigation into the source of the leak to the Mail on Sunday, Mr Trump told reporters in New Jersey: "We're 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."
In the emails, the UK ambassador to Washington 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."
Sir Kim questioned whether this White House "will ever look competent" but also warned the US president should not be written off.
Frank opinions
Dating from 2017 to the present day, the leaked emails said rumours of "infighting and chaos" in the White House were mostly true and policy on sensitive issues such as Iran was "incoherent, chaotic".
Although the Mueller investigation later found allegations of conspiracy between the Trump campaign and Russia were not proven, Sir Kim's emails said "the worst cannot be ruled out".
Foreign Secretary Jeremy Hunt said the memos reflected a "personal view", not that of the UK government.
Mr Hunt - who is seeking to become the next Conservative leader and prime minister - said it was the ambassador's job to give "frank opinions" but they did not reflect the government's view.
He said Mr Trump's administration is "not just highly effective but the best friend of Britain on the international stage".