The head of counter-terrorism within the Home Office has told MPs he was unaware of some of the GCHQ operations exposed by disclosures made by US whistleblower Edward Snowden.
Charles Farr, director general of the Office for Security and Counter-Terrorism (OSCT), said he also learned new details about the activities of the US National Security Agency (NSA) as a result of Mr Snowden's leaks.
Appearing before the Home Affairs Select Committee, Mr Farr said the leaks, published in The Guardian and several other newspapers worldwide, had made secret intelligence techniques "less effective".
Former NSA contractor Mr Snowden, who is in Russia, leaked information in May that revealed mass surveillance programmes such as the NSA-run Prism and the GCHQ-operated Tempora.
Asked by Dr Julian Huppert MP if the Snowden leaks had revealed information about GCHQ activities that he did not already know, Mr Farr said: "I'm not surprised in my own mind that I've learnt things which were new about the NSA.
"I didn't need to know them and I don't particularly need to know them now - but I do.
"I didn't learn things which were new about GCHQ capabilities - I did learn things which were new about GCHQ's specific operations and again I would not have expected or needed to know about those operations in the job that I hold."
Under the £1 billion Tempora operation, Cheltenham-based GCHQ is understood to have secretly accessed fibre-optic cables carrying huge amounts of internet and communications data and shared the information with the NSA.
Last week, the heads of the intelligence and security agencies - MI5, MI6 and GCHQ - appeared in public together for the first time in an open session of the Intelligence and Security Committee.
MI6 chief Sir John Sawers said al Qaida were ''rubbing their hands with glee'' at the exposure of the surveillance methods used by GCHQ, while GCHQ director Sir Iain Lobban said in the five months since Mr Snowden's revelations surfaced terrorist groups had discussed how to avoid communications systems they now considered to be vulnerable.
Asked by David Winnick MP if revelations that the German chancellor Angela Merkel's phone had allegedly been hacked by the NSA had aided terrorists, Mr Farr said: "It's not a matter that has involved me and I hesitate to comment on an alleged NSA operation."
But Mr Farr said he agreed with the three security chiefs.
He said: "The key point is really very simple. By revealing secret capabilities and techniques, Snowden and others, have made those techniques and capabilities less effective.
"It's actually wrong to claim that those techniques were already known to terrorists and terrorist groups. The basis of those claims, which I continue to hear, it's very unclear to me but we do not believe them to be true."
Turning to communications data legislation, which was dropped after being blocked by the Liberal Democrats, Mr Farr said GCHQ was not collecting the sort of information the Government hoped to obtain through introducing new laws.
"I know that it has been claimed that GCHQ programmes, which have been exposed by Snowden and publicised in the press, allegedly indicate that GCHQ has been collecting all the communications data that we were trying to obtain through legislation," he said.
"GCHQ has never collected the data required by the law enforcement agencies and actually other agencies in this country and it never would and it's never been considered it should collect that data either."
Earlier in the hearing, Mr Farr revealed a terror suspect who escaped surveillance by dressing in a burka had been remanded in custody three times.
It was previously thought fugitive Mohammed Ahmed Mohamed had been remanded in custody twice, most recently being released on bail in April.
However, Mr Farr told the Committee the 27-year-old was arrested in July, remanded in custody and released on bail in August.
Michael Ellis MP said Mohamed's legal team had "played the system" to keep him on the streets.