London: The spy found dead in a sports bag had been given a new identity by his MI6 bosses in the months leading up to his mysterious death.

Gareth Williams, a GCHQ codebreaker on secondment to MI6, had two passports and told his best friend that he was preparing for an undercover operation.

Details of the 31-year-old's role within the secret services are disclosed today in an interview with his confidante and childhood sweetheart, Sian Lloyd-Jones, 33.

In an interview with The Mail on Sunday, she said: "I find it difficult to see anything in his personal life which could lie behind this."

Williams was training to take on a new identity eight months before he was found dead, she said.

The maths genius was found dead two days before he was due to visit Paris with his sister.

The revelations shed new light on Williams' work which, until now, had been regarded as highly technical and carrying little risk.

Training exercise

His body was found inside a zipped and padlocked North Face holdall in the bathroom of his MI6 flat on August 23. A post-mortem was inconclusive.

"He said he was learning his new identity," Lloyd-Jones said.

"In February he said he'd be unavailable for nine days because he was on a training exercise. He'd often go away, so I didn't think any more about it."

She added that she last heard from Williams on the day he was last seen alive when he was "happy and warm and the same as he always was".