A former MI6 officer who produced a dossier making lurid allegations about Donald Trump is "terrified for his safety" after he was unmasked by an American publication.
Christopher Steele, 52, fled his home in Surrey after realising it was only a matter of time until his name became public knowledge.
A source close to Steele said that he fears a backlash from Moscow.
Steele, the co-founder of London-based Orbis Business Intelligence Ltd, prepared a 35-page document that alleged the Kremlin colluded with Trump's presidential campaign and that the Russian security services have material that could be used to blackmail him.
That material included an allegation that he paid prostitutes to defile a bed that had been slept in by the Obamas on a visit to Moscow.
The research was initially funded by Republican opponents, and later by Democrats.
Trump has branded the allegations in the dossier "fake" and has said he feels as though he is living in Nazi Germany.
He said the reports about his activities in Russia were "phoney", and voiced his suspicions the dossier was leaked.
"I think it was disgraceful that the intelligence agencies allowed any information that turned out to be so false and fake out."