"But it is also because there remains a steady flow of new recruits to the extremist cause."
There are at least 2,000 people in the UK who pose a threat to national security because of their support for terrorism, the head of MI5 has said.
Jonathan Evans said there had been a rise of 400 since November 2006.
He said children as young as 15 were being recruited for terrorist-related activity by al-Qaeda.
Resources that could be devoted to counter-terrorism were instead being used to protect the UK against spying by Russia, China and others, he added.
There had been "no decrease" in the number of Russian covert intelligence officers operating in the UK since the end of the Cold War, Mr Evans said in a speech in Manchester.
"A number of countries continue to devote considerable time and energy trying to steal our sensitive technology on civilian and military projects, and trying to obtain political and economic intelligence at our expense."
It was "a matter of some disappointment", he said, that this ongoing threat continued to take up significant amounts of equipment, money and staff.*
* It seems the "officials" who are more interested in "equality" have yet to fathom this connection to their ongoing woes.