Russia has claimed the former MI6 officer reportedly responsible for an explosive dossier on Donald Trump may still be working for British intelligence.
Christopher Steele has apparently gone into hiding after being identified as the author of the report claiming Moscow held incriminating material on the US president-elect which it could use to blackmail him.
The former spy - who runs the London-based Orbis Business Intelligence Service - is said to have originally compiled the report for political opponents of Mr Trump in Washington.
A posting on the official Twitter feed of the Russian embassy in London said MI6 officers were "never ex".
Posted over a picture showing three question marks, it said the dossier, which claimed Mr Trump's staff were in contact with Moscow in the run-up to the US presidential election, was "briefing both ways" - against Russia and the president-elect.
Earlier Downing Street refused to be drawn on whether the Government had offered any assistance to Mr Steele, who was reported to be in fear for his life after being named in US media reports.
The Prime Minister's official spokeswoman confirmed there was a "standard process" for supporting current and former holders of sensitive government posts whose identities became public.
Asked whether she could offer an assurance that the UK Government had no involvement in the creation of the dossier, she said: "Nothing I have seen suggests that," adding the media reports all related to a "former employee".
The latest claims came after a furious Mr Trump denounced the claims in the dossier as "fake news" during a tumultuous press conference in New York on Wednesday.
He accused US intelligence agencies of behaving "like Nazis" over the leak of the dossier after details were included in classified briefings to the president-elect and to President Barack Obama.
The US director of national intelligence James Clapper later said he had assured Mr Trump the leak did not come from the intelligence community.
In its Twitter posting, the Russian embassy said: "Christopher Steele story: MI6 officers are never ex: briefing both ways - against Russia and US President."
It marks the latest intervention by the embassy which has been increasingly using its Twitter feed and website to taunt western critics of Russia and President Vladimir Putin.
A web posting earlier this week referred to an "impending official anti-Russian witch hunt in Britain" involving the "British special services".
There was no sign of Mr Steele at his home in the village of Runfold, near Farnham in Surrey, where neighbours said he had been living with his wife and four children for 18 months.
Next-door neighbour Mike Hopper, who was looking after the family's three cats said Mr Steele left on Wednesday. "He did not say where he was going or when he was coming back," he said.
Mr Steele's partner in Orbis, former Foreign Office official Christopher Parker Burrows, refused to comment on the dossier but said the company would review the situation over the coming days.
"In the light of everything that has happened over the last 24 hours, I don't think it would be appropriate for me to make any comments at the moment on what has happened and whether Orbis has been involved or not, and we will review that situation over the next couple of days," he told ITV News.
The firm is based in Grosvenor Gardens, in upmarket Belgravia. Its website says it was founded in 2009 by "former British intelligence professionals" and could "provide strategic advice, mount intelligence-gathering operations and conduct complex, often cross-border investigations".
Asked at a regular Westminster media briefing whether the Government knew where Mr Steele was, Prime Minister Theresa May's official spokeswoman said: "No."
Marina Litvinenko, the widow of Putin critic Alexander Litvinenko, who was murdered in London, said Mr Steele had been put in danger by collecting such information.
She told the BBC: "I believe it is very dangerous, particularly after death of my husband, because when you just approach very specific information, particularly when this information very close to very powerful people, you might be in this line and you just easily might be killed."