A former senior KGB agent is suing MI5 over invasion of his privacy, alleging his family members were victims of a campaign of harassment and unlawful surveillance.
Judges are now investigating claims made by Boris Karpichkov that his east London home was broken into and his telephone calls and post unlawfully intercepted.
Mr Karpichkov, 51, worked as a spy for the KGB and its successor, the Russian FSB, in Latvia, where he rose to the rank of major. In 1995 he swapped sides and started passing on information to the newly independent Latvian government and its Western allies. But after Russia discovered he was a double agent he fled to live in the UK in 1998.
He claims that after initially working with MI5 and Special Branch his relationship with the UK intelligence community broke down. His refusal to co-operate any further with MI5 and Special Branch officers led to threats and blackmail over his legal status in the UK, he alleges in documents lodged with the Investigatory Powers Tribunal (IPT), which investigates complaints about the security and intelligence services, MI5 and MI6.
"They wanted to know if I still had some reliable unexposed secret informants in Latvia and Russia who could be 'reactivated'," Mr Karpichkov said.
He claims MI5 approached him in order to set him up as an agent in Spain where he was to penetrate organised crime with links to the UK. He said he was also asked to help in tracing funds from tycoon Robert Maxwell's collapsed media empire. Mr Karpichkov further alleges he was asked to provide detailed information about Russian mafia infiltration of Western businesses.
But when the security services refused to offer him any protection for his wife and two sons living in the UK the relationship broke down, he said. Central to his claim is the allegation that MI5 tried to block his application for asylum in the UK after he moved to London 12 years ago. "They described very clearly that MI5 can easily influence the Home Office's decision regarding my application for asylum and make my life miserable," he wrote.
As part of his complaint to the IPT he argues that the actions of the security service have breached his human right to privacy under article 8, which provides general protection for a person's private and family life, home, and correspondence from arbitrary interference by the state. He alleges that his home in Leyton was broken into and valuable documents removed.
He said he was forced to flee the UK to live in New Zealand for a year in 2006 after his life was threatened by Russian security services who were concerned about information he had disclosed.
After taking eight months to investigate Mr Karpichkov's claims, the IPT has asked him to shorten his claim so that it can "be better understood".
The Tribunal secretary wrote: "I look forward to your reply as soon as possible so that the investigation into your complaint and Human Rights Act claim can proceed without delay."
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