A former British security official told magistrates on Thursday that she exposed a US plan to eavesdrop on members of the UN Security Council in an attempt to prevent an illegal war leading to the deaths of British soldiers and Iraqi civilians.
Katharine Gun said she intended to deny breaching the Official Secrets Act because she had disclosed the information out of necessity.
Gun, 29, from Cheltenham, Gloucestershire in western England, appeared at Bow Street magistrates court in central London where her counsel, Ben Emmerson QC, said the case raised important issues of law and disclosure.
He said GCHQ, the UK government's intelligence and security agency for whom Gun worked, had imposed limits on what instructions she could give her defense lawyers, an action which was attacked by Amnesty International as a breach of her human rights.
Gun was charged two weeks ago, eight months after she was arrested. She was sacked from her job as a GCHQ translator in June.
She faces charges under Section 1 of the Official Secrets Act, which states that any serving or former member of the security and intelligence agencies is guilty of an offence for disclosing "any information" about their work without official authority.
However, in a case brought by lawyers acting for the former MI5 intelligence officer David Shayler, the court of appeal last year ruled that the "necessity defense" was admissible under the Official Secrets Act in the event of an imminent threat to life and limb.
"The disclosure was made by her in a sincere attempt to prevent what she believed to be an unlawful war and to save the lives of British servicemen and women and Iraqi citizens," he said.
In a statement read out after the hearing by her solicitor, James Welch, Gun said she would defend the charges against her on the basis that her actions were "necessary to prevent an illegal war in which thousands of Iraqi civilians and British soldiers would be killed or maimed."
"I have only ever followed my conscience. I have been heartened by many messages of support and encouragement that I have received from around the world," she added.
Gun was arrested after the leak of a report that the US national security agency (NSA) was conducting a "dirty tricks" operation.
The operation was directed against UN security council mem-bers as part of Washington's battle to win votes in favor of a war against Iraq.