Britain:MI5 has identified at least 2,000 people who pose a direct threat to British national security because of their support for terrorism.
The director general of the security service, Jonathan Evans, yesterday voiced his suspicion that "there are as many again" not yet known to the authorities, while warning of a "deliberate" and "dynamic" al-Qaeda campaign against Britain now promoted and encouraged from within a variety of countries beyond the tribal areas of Pakistan.
His warning about the "generation-long challenge" to defeat the terror threat came on the eve of today's queen's speech and a new counter-terrorism bill through which the British government is expected to seek to double the 28-day limit on holding terrorist suspects without charge.
Mr Evans's speech appeared unconnected to the renewed controversy over the detention period, which is regarded essentially as a police matter.
While the MI5 chief regretted having to divert resources from the fight against terror to counter spying by Russia, China and others, this address to the Society of Editors in Manchester was not seen as a plea for still more resources.
Mr Evans spoke of the daily pressures on the security service to prioritise, while emphasising the need for a strategic and long-term response to the terror threat and stressing the need to protect vulnerable young people who were being "methodically and intentionally" targeted by terrorists.
A year ago Mr Evans's predecessor, Eliza Manningham-Buller, said MI5 had identified about 1,600 individuals believed to pose a threat.
The 400 increase in that estimate was partly explained by his service's "more thorough" coverage of extremist networks.
However, he added, "it is also because there is a steady flow of new recruits to the extremist cause".
Mr Evans said they had seen the al-Qaeda campaign evolve further in that period. "As a country, we are rightly concerned to protect children from exploitation in other areas," said Mr Evans.
"We need to do the same thing in relation to violent extremism.
"As I speak, terrorists are methodically and intentionally targeting young people and children in this country. They are radicalising, indoctrinating and grooming young, vulnerable people to carry out acts of terrorism."
Another development in the past 12 months had been "the extent to which conspiracies" in Britain were "being driven from an increasing range of overseas countries".
There was now no doubt that al-Qaeda in Iraq "aspires to promote terrorist attacks outside Iraq", said Mr Evans.
"There is no doubt there is training activity and terrorist planning in east Africa - particularly in Somalia - which is focused on the UK.
"And there is no doubt that the extension of what one might call the 'al-Qaeda franchise' to other groups in other countries - notably in Algeria - has threatened a significant upsurge in terrorist violence in these countries."
Mr Evans continued: "This sort of extension of the al-Qaeda brand to new parts of the Middle East and beyond poses a further threat to us because it provides al-Qaeda with access to new centres of support which it can motivate and exploit, including in its campaign against the UK".
On a different note, Mr Evans looked forward to the official opening of MI5's new Northern Ireland headquarters by the secretary of state.
Mr Evans said: "This new building is a regional headquarters concerned with the broad spectrum of MI5's work. So although we will continue to investigate national security threats to Northern Ireland from there, the capabilities will also provide us with greater capacity in our overall work across the UK."
MI5 took on the lead responsibility for national security from the PSNI on October 10th.
Mr Evans yesterday quoted deputy assistant commissioner Peter Clarke, head of the Metropolitan Police's Counter Terrorism Command, saying that the most important change in counter-terrorism in the UK in recent years had been "the development of the relationship between the police and the security service".