A "damaging public debate" over GCHQ's spying activities could lead to legal challenges against its mass-surveillance programmes, the intelligence agency fears.
Classified documents leaked by the US whistleblower Edward Snowden outline GCHQ's ongoing battle against having evidence obtained through interception being allowed as evidence in court.
According to the Guardian, the leaked memos revealed the agency was keen to reduce the possibility of challenges against its wide-scale interception programmes.
GCHQ Headquarters, the British eavesdropping agency
It feared challenges under the Human Rights Act to the right to privacy if its methods became admissible in court.
Four years ago the intelligence agencies GCHQ, MI5 and MI6 defeated an attempt to make intelligence gathered from intercepts admissible in court, the Guardian said.
A note prepared for the GCHQ board before the decision was made public revealed that it was keen to prevent the proposals because of fears that even passing references to its surveillance powers could start a "damaging" public debate.
On the decision to publish the report about interception as evidence without classification, it said: "Our main concern is that references to agency practices (interception and deletion) could lead to damaging public debate which might lead to legal challenges against the current regime."
Earlier this week, it emerged that America's National Security Agency (NSA) had monitored the telephone calls of at least 35 world leaders, using numbers obtained by officials in other US government departments.
Germany's chancellor Angela Merkel and French president Francois Hollande have both called for talks with the US administration before the end of the year to resolve the dispute and rebuild trust.
Shami Chakrabarti, director of Liberty and Anthony Romero executive director of the American Civil Liberties Union issued a joint statement stating: "The Guardian's publication of information from Edward Snowden has uncovered a breach of trust by the US and UK Governments on the grandest scale. The newspaper's principled and selective revelations demonstrate our rulers' contempt for personal rights, freedoms and the rule of law.
"Across the globe, these disclosures continue to raise fundamental questions about the lack of effective legal protection against the interception of all our communications.
"Yet in Britain, that conversation is in danger of being lost beneath self-serving spin and scaremongering, with journalists who dare to question the secret state accused of aiding the enemy."
Pressure mounted this week as Index on Censorship and a coalition of freedom of speech charities delivered a petition to the President of the European Council, Herman Van Rompuy demanding that the EU take a stand against mass surveillance by the US and other governments.
Thousands of signatories included writer and actor Stephen Fry, activist Bianca Jagger, writer AL Kennedy, artist Anish Kapoor and blogger Cory Doctorow.