A dossier of embarrassing allegations about Donald Trump produced by a former British spy "probably" has "some credibility", the ex-head of MI6 has said.

Christopher Steele, himself a former MI6 officer, compiled the dossier in which he claimed Russia held compromising information on the US president which left him vulnerable to blackmail.

At the time, Mr Trump denounced the document as fake news, and its veracity has widely been questioned.

But Sir Richard Dearlove, who ran MI6 between 1999 and 2004, told BBC's Newsnight programme: "I think that there is probably some credibility to the content.. I wouldn't put it any more forcefully than that."

Among the more lurid allegations was a claim that the Russians held evidence of Mr Trump hiring prostitutes during a visit to Moscow to urinate on a hotel bed which he believed Barack and Michelle Obama had previously slept in.

The file also claimed that the Trump campaign team had multiple contacts with Russian officials during the presidential election race.

The President has repeatedly denied any collusion with Russia.

Sir Richard, who backed Leave in Britain's referendum on European Union membership, said there was no evidence of Russian intervention in the Brexit vote, but that it interfered in the US election.

He said: "I've not seen anything that convinces me at all that the Russians intervened significantly in the Brexit referendum ... I don't think there's any question that they got involved in the US election."

Sir Richard Dearlove, former head of MI6 credit: Martin Pope

He added: "I think probably on Putin's part, you know, that was a misjudgment."

Mr Trump's former national security adviser Michael Flynn has since pleaded guilty to lying to investigators during an FBI investigation into potential links with Moscow.

In October it was reported that FBI investigators had met with Mr Steele the previous summer.

"CNN has learned that the FBI and the US intelligence community last year took the Steele dossier more seriously than the agencies have publicly acknowledged," the network reported on its website.

The investigation has been criticised by Republican figures, including Mr Trump, who has described it as a "witch hunt".

View more!

It has also been suggested that Hillary Clinton's presidential campaign helped to fund the research that led to Mr Steele's dossier.

Marc Elias, a lawyer representing the Clinton campaign and the Democratic National Committee (DNC) used the Washington-based private intelligence firm, Fusion GPS, to conduct the research, the Washington Post reported.

Fusion GPS is then said to have employed Mr Steele, a former MI6 officer, who produced the dossier. The report did not state how much Fusion GPS was paid for the work.