The number of terror suspects being detained has reached a record level, driven by dramatic rises in arrests of women and children.
Home Office figures showed there were 315 terrorism-related arrests in the year ending September 2015, an increase of a third on the previous year.
Arrests of females more than doubled on the previous year to 50, while the number of under-18s jumped from eight to 15.
There was also a 31% increase in arrests for international-related terrorism.
Security services and police are mounting an unprecedented effort to counter the threat from terrorism following the rise of Islamic State.
The statistics bear out warnings about increasing numbers of women and teenagers being drawn into extremism.
Schoolgirls and young families are among those feared to have fled the UK to join IS, also known as Isil or Daesh.
Females accounted for around one in six (16%) of the total counter-terrorism arrests throughout the year - a rise of 7 percentage points on the previous 12 months.
Since the 9/11 attacks in 2001, only 8% of all those detained for terrorism-related offences have been female, but one in five of all the arrests of women or girls have occurred in the last year.
The Home Office report said: "The majority of the increase in the number of women getting arrested has been linked to international-related terrorism."