The widow of poisoned former Russian spy Alexander Litvinenko says she fears for the life of the British ex-MI6 agent named as the man behind the discredited 'dirty dossier' on Donald Trump.

Marina Litvinenko's husband - an outspoken critic of Vladimir Putin - died in London after drinking tea laced with radioactive polonium-210 in 2006.

Now she fears Christopher Steele is in grave danger, telling The Sun: 'It is very dangerous when you approach very specific information, particularly when this information is very close to very powerful people, you might easily be killed.'

Former spy Steele has been named as the author of the salacious Russian dossier containing outlandish claims about President-elect Trump's sex life and bizarre footage allegedly held by the Kremlin's blackmail unit.

Marina Litvinenko, widow of Russian former spy Alexander Litvinenko, says she fears for the life of British ex-MI6 agent Christopher Steele who authored the Trump 'dirty dossier'

The 35-page briefing, which is littered with spelling mistakes, includes an unsubstantiated and far-fetched claim Trump watched prostitutes perform a 'golden shower (urination) show' in the Presidential Suite of a Moscow hotel.

Mr Trump called the dossier 'fake' and 'phony', even suggesting that US secret services had leaked it to damage his reputation before his inauguration.

He debunked the 'golden shower' claim by saying: 'Does anyone believe that? I'm a germophobe'.

Steele, 52, was seen fleeing his gated Surrey home in his car on Wednesday and appears to have been in such a rush most of the lights were left on.

A security source said: 'He is terrified for his safety', adding he may now be abroad or in a safe house.

A neighbour told the Telegraph: 'He asked me to look after his cat as he would be gone for a few days'.

Former spy Christopher Steele has been named as the author of the salacious Russian dossier containing outlandish claims about President-elect Trump

Alexander Litvinenko is pictured at the Intensive Care Unit of University College Hospital on November 20, 2006 in London. The 43-year-old former KGB spy died three days later and accused Russian President Vladimir Putin of involvement of his death

Steele served MI6 for nearly two decades in Moscow - and a stint in its Paris Station - and security sources say he once worked with murdered Litvinenko who fled to Britain before he was poisoned in 2006.

Litvinenko's wife Marina said earlier this week that she did not recognise the name Steele but admitted MI6 agents often have a number of different identities.

Steele was employed by enemies of Trump to dig for 'dirt' in Russia having previously worked for the FBI in helping uncover corruption at FIFA, which led to the arrest of its leadership including Sepp Blatter.

Marina last year said she has not given up hope of securing justice for her husband.

A public inquiry concluded earlier in 2016 that the killing of Litvinenko had 'probably' been carried out with the approval of the Russian president Vladimir Putin.

In a statement to mark the 10th anniversary of his death, Marina said her husband - who she called Sasha - had been an 'extraordinary man' whose courage in speaking out against the Russian security service, the FSB, had left an enduring legacy.

US President-elect Donald Trump (C) and US television host Steve Harvey (R) are seen in the lobby of Trump Tower in New York on January 13 after the discredited dossier was released

Marina Litvinenko, the wife of former Russian spy Alexander Litvinenko, with her son Anatoly after the findings of the inquiry into the former KGB spy's death were revealed

While she acknowledged Putin had refused to accept the inquiry's findings, she said it remained open for other world leaders to take action against the Russian state and that she hoped her struggle to find the truth had not been in vain.

'It has taken 10 long years for the truth to be established and for Sasha's dying words that President Putin was responsible for his death to be proved to be true,' she said.

'I know that Mr Putin's Russia does not accept the findings of the British public inquiry and will continue to deny the truth in the face of overwhelming evidence.

'But those findings are now part of history and the rest of the world understands the difference between truth and propaganda. And that is what matters to me.'

The inquiry headed by the former high court judge Sir Robert Owen found two Russian men - Andrei Lugovoi and Dmitri Kovtun - had deliberately poisoned Litvinenko by putting polonium-210 into his drink at a London hotel, leading to an agonising death.

It said the use of the radioactive substance - which could only have come from a nuclear reactor - was a 'strong indicator' of state involvement and that the two men had probably been acting under the direction of the FSB.

Possible motives included Litvinenko's work for British intelligence agencies, his criticism of the FSB, and his association with other Russian dissidents, while it said there was also a 'personal dimension' to the antagonism between him and Putin.

International arrest warrants issued for Lugovoi and Kovtun remain in force although Russia continues to refuse their extradition.