Alleged Russian spy Katia Zatuliveter, who had an affair with a Member of Parliament, has won her fight to avoid expulsion.

Zatuliveter, 26, who worked as a parliamentary aide for former UK defence select committee member Mike Hancock, 65, was granted permission to remain in the country at a hearing behind closed doors by the Special Immigration Appeals Commission (SIAC) on Tuesday.

Our conclusion, at least on the balance of probabilities, is that she was and is not a Russian agent, official court documents said.

The Home Office, which had ordered her expulsion, said it was disappointed by the ruling.

Zatuliveter has been at the centre of media speculation in the UK over the past year after she was accused being a 'sleeper agent' for Russian intelligence services.

The allegations were made just months after Russian spy Anna Chapman was expelled from the United States, ramping up political tensions between Western powers and the former Soviet Union.

Hancock, who is MP for Portsmouth South, where there is a large naval base, had denied his research assistant had done anything wrong.