MI6 agent Gareth Williams was vulnerable to blackmail, having carried out unauthorised searches on spy computers, an inquest heard today.

A malign or hostile party could have "theoretically put some pressure on to Gareth", his boss said.

But a Secret Intelligence Services' inquiry ruled out any connection with the discovery of his body in a bag and his "world class" work.

Relatives of the spy walked out of the inquest into his death in tears as MI6 apologised for blunders which saw colleagues fail to raise the alarm about his disappearance for seven days.

The witness, named to the inquest as SIS F, said she was "profoundly sorry" after family lawyer Anthony O'Toole said the agency showed a "total disregard for Gareth's whereabouts and safety".

SIS F blamed Mr Williams' line manager for the "breakdown in communication".

She denied family fears that the "dark arts" of the secret services had been involved in a cover up.

When asked what justification Mr Williams might have had for unauthorised searches, she said: "It seems to me that there was less to this than meets the eye."

She added that a review confirmed there was "no evidence of any specific threat to Gareth and we concluded that there was no reason to think his death was anything to do with his work".

She said Mr Williams was "a fully deployable, highly talented officer" who had passed exams to do some of MI6's toughest covert work six months before he was found dead on 23 August, 2010.

His examiner said in a report: "I was particularly impressed with Gareth. This was definitely the most intense operational course that I have seen and the improvement needed was immense."