Tony Blair today insisted that Britain's intelligence services always act within domestic and international law.
And he turned on the former International Development Secretary Clare Short after she claimed that British agents spied on United Nations Secretary General Kofi Annan in the run up to the war on Iraq.
Mr Blair said those who comment on national intelligence "attack the work that our security services are doing and undermine the security of this country".
And he added: "The fact that these allegations were made is deeply irresponsible."
The Prime Minister, who described Mr Annan as a personal friend for whom he had great respect, refused to comment directly at the monthly televised press conference at No10 on Ms Short's claims.
Downing Street announced later that the Government is to review the working of the Official Secrets Act following the collapse of the case against ex-GCHQ worker Katharine Gun.
Mr Blair said his refusal to comment on Ms Short's allegations should not be taken as an indication that her were true.
He said: "I hope the country understands. It is very tempting to see people who want to talk about the work of our security services as so-called whistleblowers or people simply in favour of open information. But I tell you our security services, particularly today, particularly with global terrorism as it is, perform an absolutely vital task on behalf of this country.
"Many of their people work in circumstances of very great danger and it really is the height of irresponsibility to expose them to this type of public questioning and scrutiny in a way that can do absolutely no good to the security of this country."
Mr Blair said if he confirmed or denied specific allegations it would open the floodgates. He said he had absolutely no doubt conspiracy theorists would now say it was all "some terrible plot".
Mr Blair was asked whether Ms Short should remain a Labour MP. He said: "These are issues I will have to reflect upon."
Mr Blair also said he would not discuss the case of former intelligence service worker Katharine Gun, who was acquitted yesterday of breaching the Official Secrets Act despite admitting leaking a US request for help in bugging the UN.
Discussing the work of the intelligence services would undermine national security, Mr Blair claimed.
"I will simply not let that happen," he said.
Earlier, the Attorney General Lord Goldsmith insisted the case against the GCHQ whistleblower Katharine Gun was dropped purely in the public interest. He said the decision not to proceed with the prosecution was not taken to spare the Government's embarrassment.
In a statement in the House of Lords Lord Goldsmith said he was responsible for giving the go-ahead for the prosecution of Ms Gun. The case was dropped, he said, because the Crown Prosecution Service later decided there was no realistic prospect of a conviction.
Her lawyers have speculated it was because they had demanded the Government disclose advice it received from the Attorney General on the legality of going to war in Iraq.
Disclosing it to Mrs Gun's legal team could have led to the Government facing fresh public scrutiny of the case for war, but withholding it would have allowed Mrs Gun to argue she could not receive a fair trial.Reuse content