Chapman's friends and business associates are being investigated to see if she recruited them as sub-agents. I5 is also enquiring if she had links to agents working undercover at the Russian Embassy in London.
MI5 took action after US authorities charged Chapman and nine others with spying for Russia in a 'deep-cover' operation, reports The Sun. Chapman's ex-husband Alex feels she might have been recruited while living in London.
Her friend Oleg Gordievsky believes a Russian diplomat groomed her.
The 28-year-old spy spent five years living in Britain, during which she became a British citizen.