Theresa May’s spy chiefs were secretly briefed on an explosive dossier of claims about Donald Trump’s ties to Russia before the US president was made aware of its existence, The Telegraph can reveal.

The heads of MI5 and MI6 and one of Mrs May’s most trusted security advisers were told about former British intelligence officer Christopher Steele’s memos on the Trump campaign in the weeks after his November 2016 election victory.

Mr Trump himself would only learn of the document, which included an allegation strenuously denied by Mr Trump that he hired prostitutes to perform a lurid sex act in a Moscow hotel, in January 2017 when alerted by the FBI before taking office.

The disclosure risks deteriorating UK-US relations ahead of Mr Trump’s state visit next month.

The US president has previously tweeted a claim that Britain’s intelligence services helped spy on his election campaign.

The seriousness with which the dossier was handled, being elevated to the country’s most senior intelligence figures, also suggests it was treated with gravity - in contrast to Mr Trump’s stance that the document is “fake” and “phony”.

Number 10 sources insist that Mrs May was never briefed on the Steele memos herself - indicating that intelligence chiefs decided to keep her at arm's length from the information, though why exactly remains unclear.