A GCHQ translator sacked for revealing a secret e-mail has been cleared of a charge under the Official Secrets Act.
Katharine Gun said the e-mail asked for help bugging key states
Katharine Gun, 29, from Cheltenham, claimed the e-mail was from US spies asking British officers to tap phones of nations voting on war against Iraq.
She walked free on Wednesday when the prosecution offered no evidence.
Ms Gun had always said she had acted in an effort to prevent the war, and outside court said: "I have no regrets and I would do it again."
The leaking of the e-mail to the Observer newspaper generated a row and saw Ms Gun's case become a cause celebre in the US, with civil rights activist Jesse Jackson and actor Sean Penn lending their support.
Human rights group Liberty, which supported Ms Gun throughout her trial, said it was possible the prosecution's decision followed political intervention.
There has been speculation the government was worried about the disclosure of secret documents during the trial, particularly the advice by Attorney General Lord Goldsmith about the legality of war.
Under the Official Secrets Act, the attorney general has the final decision on whether or not to prosecute.
But the attorney general's office told the BBC the decision to drop the charge had nothing to do with Lord Goldsmith's advice.
Ms Gun's legal team served documents on the government on Tuesday demanding to see any advice given to ministers about the legality of the war.
But BBC political correspondent Guto Harri said a government spokesperson insisted the decision to drop the case was taken before the demand for documents was made.
The same spokesperson suggested the case might have been dropped as Ms Gun planned to argue she leaked the e-mail to save lives from being lost in a war, something that could persuade a jury and would lead to the reputation of the Official Secrets Act being damaged.
Our correspondent said this suggested the government had made a political calculation that a random selection of a dozen jurors would be likely to be so instinctively anti-war than an acquittal would be likely.
Ms Gun, who was sacked from GCHQ in June and charged on 13 November, thanked her family and friends for helping her through the case.
She told a news conference: "Obviously I'm not prone to leak secrets left, right and centre... but this needed to get out, the public deserved to know what was going on at the time.
"I was pretty horrified and I felt that the British intelligence services were being asked to do something that would undermine the whole UN democratic processes."
Ms Gun revealed she was strongly anti-war but said she had not been looking for a piece of information to leak and embarrass the government.
"I'm just baffled in the 21st century we as human beings are still dropping bombs on each other as a means to resolve issues."
The memo, from January last year, reportedly said the National Security Agency had begun a "surge" in eavesdropping on UN Security Council countries crucial to the vote on a second resolution for action in Iraq.
Officials from Angola, Cameroon, Chile, Bulgaria, Guinea and Pakistan all had their phones tapped in what the Observer described as a "dirty tricks" operation.
BBC security correspondent Frank Gardner said managers within the intelligence service might now be thinking about talking to members of staff about their concerns to prevent future whistle-blowing.
Shami Chakrabarti, of Liberty, said the decision to charge Mrs Gun in the first place had been political.
"One wonders whether disclosure in this criminal trial might have been a little too embarrassing," she said.
The Liberal Democrats' foreign affairs spokesman Sir Menzies Campbell said: "It is possible the attorney general's legal advice might have been published at last.
This is a government retreat.''
Ms Gun pleaded not guilty on Wednesday, after which the prosecution announced it would not be going ahead with its case.
Mark Ellison, for the prosecution, said: "There is no longer sufficient evidence for a realistic prospect of conviction.
"It would not be appropriate to go into the reasons for this decision."
The judge, the Recorder of London Michael Hyam, recorded a formal verdict of not guilty.
The defence inquired why it took until Wednesday for the case to be dropped, but the prosecution offered no explanation.
They also want to know why news of the charges being dropped was apparently leaked to the Guardian newspaper last week.
All that is needed for a successful prosecution under the Official Secrets Act is for the prosecution to demonstrate the accused is covered by it, which Ms Gun was, and they have revealed information covered by it, which she also admitted.
Her solicitor James Welch described the prosecution's excuse as "rather lame".
Former spy David Shayler, jailed for revealing secrets, said a blanket of secrecy was used to protect intelligence matters that did not affect national security.
"If the intelligence services are going to do things that are illegal they have to expect people to whistle-blow."