MPs have warned that the preparations for the London Olympics have put the intelligence and security agencies under "unprecedented pressure."
The parliamentary Intelligence and Security Committee (ISC) - which oversees the work of MI5, MI6 and GCHQ - expressed concern that risks were been taken with other aspects of security because of the demands of the Olympics.
Staff have been taken off lower priority areas of work so that they can concentrate on the potential threat to the Games.
The family of MI6 spy Gareth Williams have hit out at the failures of MI6 to raise the alarm after the spy went missing, saying their "grief is exacerbated" by it.
In a statement read out by their solicitor after the inquest into his death concluded, they said they were "extremely disappointed" at the secret services' "reluctance and failure" to make relevant information available to the death inquiry.
They also attacked the "total inadequacies" of the inquiry by Metropolitan Police counter-terror branch SO15 into MI6 and called on Scotland Yard's chief to look into how the investigation would proceed in light of this.
Secret agents specialising in the "dark arts" might have tried to cover up the death of an MI6 spy found in a holdall, a coroner has heard.
Relatives believe a third party was either present when Gareth Williams died or broke into his home afterwards to destroy evidence, lawyer Anthony O'Toole said.
The family is demanding answers after Scotland Yard revealed a key line of its inquiries had been an 18-month DNA mix-up.
Mr O'Toole told a pre-inquest review that Westminster Coroner's Court must establish why there was no evidence of another person in his London apartment when he died.
He said: "The impression of the family is that the unknown third party was a member of some agency specialising in the dark arts of the secret services - or evidence has been removed post-mortem by experts in the dark arts."