MI6 spy Gareth Williams, whose dead body was found in a padlocked red bag in his central London home in 2010, was allegedly murdered by Russian hitmen for refusing to become a double agent, a former KGB major has claimed.

Former intelligence officer Boris Karpichkov, 56, a onetime major in the KGB, claims his information came from sources high up in the Russian intelligence services.

Williams, 31, was a codebreaker for Government Communication Headquarters (GCHQ) but was on secondment to MI6 in Vauxhall at the time of his death.

The Welsh-born spy lived in an MI6 flat in Pimlico, near the organisation’s HQ in Vauxhall.

No fingerprints or DNA belonging to the spy were found on the rim of the bag and there was no sign of a break-in.

In 2012, a coroner ruled that Williams was “probably killed unlawfully,” but added that it was unlikely his death would ever be “satisfactorily explained.”

Karpichkov, who was exiled from Russia and now lives in the UK under a new identity, is certain he has unraveled the mystery behind the 31-year-old’s death.

He told the Daily Mail that a Russian double agent working at GCHQ was determined to recruit Williams to work for Russian foreign intelligence service, the SVR.

It is believed that hitmen found their way into Williams’ London flat and killed him through a poisonous injection in his ear. Boris Karpichkov claimed Mr Williams was given a lethal injection in the ear

The British spy's family insist that he didn’t die alone; RT reported.