Britain has been dragged into the frantic row over the “dirty dossier” on Donald Trump after it was claimed that the Government gave the FBI permission to speak to the former MI6 officer who compiled it.

Sources in the US have told The Telegraph that Christopher Steele, a former spy, spoke to officials in London before he handed the document to the FBI and met one of its agents.

The dossier contained allegations about President-elect Trump credit: Seth Wenig /AP

The document, which contained allegations of lurid sexual behaviour by Mr Trump in Russian hotels, was leaked earlier this week, and Britain now finds itself caught in the crossfire of accusations between Russia and the US.

On Thursday Russia publicly accused MI6 of “briefing both ways” against Russia and Mr Trump and suggested Mr Steele was still working for the Secret Intelligence Service.

The Russian embassy in London used its official Twitter account to say: “Christopher Steele story: MI6 officers are never ex: briefing both ways – against Russia and US President.”

Mr Trump has angrily rejected the information in the dossier as “fake” and the involvement of a former MI6 officer is unlikely to help Britain’s intelligence-sharing relationship with the US when he becomes president later this month.

Mr Steele, who friends say fears for his safety, has gone into hiding while the veracity of the claims made in his dossier, and his own reputation, continue to be fiercely debated.

Sir Tony Brenton, a former British ambassador to Russia, described the dossier as looking "pretty shaky". He told Sky News: "For example, it claims that the Russians began to cultivate Donald Trump five years ago.

"If they did that they showed remarkable prescience because at the time he had nothing to do with American politics."

It emerged that he was the MI6 case officer assigned to Alexander Litvinenko, the former FSB agent murdered in London with a radioactive substance.

Mr Steele was the MI6 case officer in the Litvinenko poisoning credit: PA

Mr Steele was hired to find information on Mr Trump by a Washington-based consultancy that was being paid by Republican opponents of the president-elect – the BBC claimed they were acting on behalf of fellow nominee Jeb Bush – and, later, by Democrats.

However, he decided the information was so sensitive that it should also be passed on to the FBI and to his old colleagues at MI6.

The Daily Telegraph was told during a meeting with a highly-placed source in Washington DC last October that the FBI had contacted Mr Steele asking if they could discuss his findings with him. The source said that Mr Steele spoke to officials in London to ask for permission to speak to the FBI, which was duly granted, and that Downing Street was informed.

Mr Steele was an MI6 officer credit: Anne-Marie Palmer /Alamy

Downing Street and the Foreign Office refused to comment, while security sources said that it would have been a “professional courtesy”, though not an absolute requirement, for Mr Steele to seek permission for a meeting with the FBI.

Once he had been given the all-clear, he met an FBI agent in another European country, where he discussed the background to the file he had compiled. His contact with the FBI reportedly began in July last year and ended in October, after he became frustrated by the bureau’s slow progress.

Dominic Grieve, chairman of the Commons intelligence and security committee, said he expected the committee to discuss the fallout from the dossier and the question of whether British intelligence agencies had been involved in handling it.

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The FBI declined to comment, and the US embassy in London did not respond to requests for comment.

As the row over the dossier continued, the US vice-president Joe Biden said the FBI had felt obliged to tell President Barack Obama about the information it contained because of concerns it would go public and catch the president off guard.

Mr Biden said neither he nor Mr Obama asked US intelligence agencies to try to corroborate the unverified claims that Russia had obtained compromising sexual and financial allegations about Mr Trump.

Members of the US intelligence community have said it would have been a “dereliction” of duty not to mention allegations that the Russians had material with which they might try to blackmail Mr Trump.