Former Labour Lord Chancellor Lord Falconer has downplayed the extent to which Guardian stories based on the Edward Snowden leaks have damaged national security.
A succession of senior Government and intelligence figures have claimed that detailed revelations about the spying activities of GCHQ have undermined their ability to protect Britain from terrorism.
But in a Guardian interview, Falconer said: "I am aware that the three heads of the agencies said what has been published has set back the fight against terrorism for years. Sir John Sawers [the chief of MI6] said Al Queda would be rubbing their hands with glee. This is in the context of maybe 850,000 people literally having access to this material."
Falconer, who is in charge of Ed Miliband's preparations for government, added: "It seems to me to be inconceivable that the intelligence agencies in the US and the UK were not aware that it would not be possible to keep secret these sorts of broad issues for any length of time. If the position was that the USA and the UK were intending to keep the general points I have been talking about secret then that seemed to me to be a very unrealistic position.
"Although I take very seriously what they say [about the importance of secrecy] I am sceptical that the revelations about the broad picture have necessarily done the damage that is being asserted."
Guardian editor Alan Rusbridger is to appear before the House of Commons home affairs committee next month to defend his newspaper's conduct.