Ms Machon, 29, a former MI5 agent who left the secret service at the same time as Mr Shayler, was arrested at Gatwick Airport on Saturday as she flew into Britain.
Mr Shayler caused political controversy after describing the management incompetence and ineptitude he witnessed during his seven years in the secret service. His account was published in a Sunday newspaper and he and Ms Machon later left the country for a secret location.
The Government was granted an injunction preventing Mr Shayler from making further disclosures about MI5, but Ms Machon later gave an interview supporting everything Mr Shayler had said. He claimed that MI5 held files on Peter Mandelson, Minister without Portfolio, and Jack Straw, the Home Secretary.
Ms Machon is believed to have alerted police to her return from Barcelona at the weekend and was questioned for six and a half hours at Charing Cross police station before being released without charge on police bail.
John Wadham, the solicitor representing the couple, said: "The authorities should be concentrating on finding ways of making MI5 more accountable rather than arresting and questioning my client."Reuse content