A record 315 terror suspects have been arrested in the past year, with dramatic increases in arrests of women and teenagers.

The number of women arrested for terrorism-related offences more than doubled in the 12 months to September from 21 to 50, while the number of under-18s detained reached 15 – its highest ever level.

The 31% rise in the number of suspects arrested for international-related terrorism reflects an unprecedented effort by the police and security services to counter the threat from Islamic State and the flow of British citizens to and from Syria.

According to the Home Office quarterly bulletin, the rise in the number of women arrested as terror suspects means they now account for 16% of all such arrests. The bulletin adds that normally women or girls only make up 8% of those arrested, and one in five of all arrests of female terror suspects in Britain since the 9/11 attacks 14 years ago have happened in the last year.

“The majority of the increase in the number of women getting arrested has been linked to international-related terrorism,” the report said.

The figures show the rise included a 41% increase in those who considered themselves Asian and a 25% increase in those who considered themselves white. The proportion of terror suspects who are British has risen sharply to 79% of those arrested this year, compared with 56% in 2001 when the statistics were first collected.

The detailed Home Office figures for the 12 months to September 2015 show that nearly 40% (124) of those arrested have been charged, a further 22% (68) were released on bail, and 37% (115) were released without charge.

The 37% arrested then released without charge is a slight increase over the previous year’s 31% but far below the 53% who were detained and released in 2013.

The Home Office said the 31% rise in terror suspects arrested was driven by a particularly large number of arrests in two quarters: October to December 2014 and April to June 2015. “The most recent quarter saw a fall in the number of arrests to around half that of the quarter before (94 down to 48),” the report said.

The bulletin says the wide-ranging nature of terrorism investigations that the police undertake can lead to fluctuations in the number of arrests from one quarter to the next: “Furthermore, individual investigations involving multiple suspects are likely to cause an increase in the figures more than investigations involving small numbers of suspects,” it adds.



The security minister, John Hayes, said: “We are determined to detect, disrupt and where possible prosecute all terrorist threats to the UK. The figures released today once again highlight the hard work carried out by the police, security service and crown prosecution service to keep the public safe – and emphasise the scale of that challenge.

“At a time of very significant threat, it is vital they have the powers they need to protect the British public. The counter terrorism and security act has enhanced our powers to disrupt the ability of people to travel abroad to fight, reduce the risks they pose on their return and combat the underlying ideology that feeds, supports and sanctions terrorism.”

The Royal United Services Institute said 289 people were detained on suspicion of terrorism offences in 2014, nearly 20 fewer than the previous 12 months, and 102 went on to be charged.

The defence and security thinktank said the proportion of arrests leading to charges was “substantially lower” for terrorism offences than for criminal offences generally, at 35% compared with 58%.

A spokesman said: “The number of arrests is often quoted as an illustration of the scale of the threat. However, it more accurately demonstrates the scale of police activity in countering it. Charge or conviction data would be a better measure of the level of confirmed terrorist activity.”

But the Home Office bulletin says it is difficult to compare charge rates on a like-for-like basis until all the cases within a given time period have been completed.