Today, the Special Immigration Appeals Commission (Siac) announced it had seen no evidence proving Katia Zatuliveter was a spy with a mission to seduce Hancock and steal secrets.

Zatuliveter worked as a parliamentary researcher for the 65-year-old Portsmouth South MP. 

The panel of judges, which included the former MI5 chief Sir Stephen Lander, said that her relationship with the MP had been “enduring and genuine”.

The judges were told that MI5 assessed that Miss Zatuliveter had been placed in Mr Hancock’s office by Russian agents because he was a member of the Commons defence select committee.

Hancock, a backbench MP, said he only saw defence documents which were in the public domain and denied passing any secrets on to the Russian, with whom he had a four-year affair. 

Siac found Zatuliveter had not been liaising with Russian spies from either the FSB or SVR agencies and that even if she had, “we have seen nothing which satisfies us that she was recruited as an agent or was tasked, or acted, as one”.

Zatuliveter’s solicitor, Tessa Gregory, denounced the “amateur” nature of the case against her client.

Siac dismissed criticisms of MI5, which was described by Zatuliveter’s counsel Tim Owen QC as acting “more like Inspector Clouseau than George Smiley”.

The Home Office said it was disappointed.

 Miss Zatuliveter has a visa to stay in the UK until August 2012.