A former head of MI5 believes the United States will seek a deal with whistleblower Edward Snowden to prevent him divulging more secret intelligence material.
Eliza Manningham Buller said she was opposed to the publication of files leaked by the former CIA agent because newspapers could not know what damage it had done to counter-terrorism operations.
Mr Snowden, who embarrassed Washington and London by revealing the existence of mass surveillance programmes, is now in Russia, which granted his temporary asylum after he fled the US.
Asked if he should face prosecution, Ms Manningham Buller told BBC Radio 4's 'Today': "I think what will happen actually is some kind of deal that he doesn't release any more but I really don't know."
The ex-security chief, who was guest-editing the programme, said: "I do understand that there are people who think he has done a public service and who applaud him but I can't really be one of them because what neither the 'Guardian' nor really anyone, including me, can judge is what damage he has done to counter-terrorism."
It was impossible for anybody other than the security services to know what terror plots had "gone dark" as a result of the information being made public or which might "not now be investigated, not now be thwarted", she said.
"My concern is the damage, which I don't think anybody outside of the intelligence community can really detect or judge," she added -- suggesting the thrust of the activities could have been published "without revealing the scale".
"I don't think those who have published can possibly work out what those consequences are because they don't have access to the information."
She said: "The debate should not be what the capability of the state is, because the terrorist has that capability. But what should be authorised and who does the authorisation and what are the limits on it."
Meanwhile, a federal judge in New York has ruled that the National Security Agency's (NSA) controversial programme to collect Americans' telephone records is lawful and has been crucial in fighting terrorism since the September 11 attacks.
The ruling comes days after a federal judge in Washington ruled that the same programme was "almost certainly" illegal and "Orwellian" as it broke constitutional rights to privacy.
The conflict between the two courts means that it is likely that the challenges to the NSA's phone data programme will be resolved by the Supreme Court.
The new ruling is a boost for America's spy agencies and the White House, which have been under relentless fire since the series of leaks by Mr Snowden, the former NSA contractor.
Judge William Pauley dismissed a lawsuit by the American Civil Liberties Union demanding a halt to the programme.
"The natural tension between protecting the nation and preserving civil liberty is squarely presented by the government's bulk telephony metadata collection programme," he wrote in his 53-page ruling.
"This blunt tool only works because it collects everything. While robust discussions are under way across the nation, in Congress and at the White House, the question for this court is whether the programme is lawful. This court finds it is."
Judge Pauley said he found no evidence that the government used any of the bulk "metadata" for any purpose other than investigating and disrupting terrorist attacks.
He said the vacuuming of metadata allowed "the NSA to detect relationships so attenuated and ephemeral they would otherwise escape notice. As the September 11 attacks demonstrate, the cost of missing such a thread can be horrific".