Record numbers of children are being arrested on suspicion of terrorism-related offences, new figures have revealed.
Sixteen under-18s were held in the year ending December, a rise from 10 in the previous year.
This was the highest number of arrests for the age group in a calendar year since data collection started in 2001.
The figures, published by the Home Office, showed there were a total of 280 terrorism-related arrests in 2015. This was a fall of 3% compared with the previous year.
The statistics also showed that rising numbers of women are being arrested as part of counter-terrorism probes.
Last year 45 female suspects were held - an increase of 15 on 2014. This continues an "upward trend" seen in recent years, statisticians said.
A Home Office report published alongside the figures said the overall fall in arrests was driven by a drop in the numbers held for domestic terrorism.
By contrast there was a small rise in arrests linked to international terrorism, which now accounts for more than three-quarters (79%) of all arrests.
Police and security services have been mounting an unprecedented operation to counter the threat to the UK following the rise of Islamic State.
Last week, Mark Rowley, the country's most senior counter-terrorism officer, warned that the group "has big ambitions for enormous and spectacular attacks". Authorities have foiled seven plots to attack the UK in the last 18 months.
The statistics released on Thursday chime with fears of 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, which is also known as Isil or Daesh.
The number of suspects who were bailed to return pending further investigation jumped nearly five-fold, from 13 in 2014 to 64 last year, accounting for 23% of the total arrests.
"As time passes, cases will progress, meaning that the number of persons released on bail will decrease, while the number of charges (and other outcomes) will increase," the Home Office report said.
Of the other people arrested, 96 (34%) were charged with an offence, 109 (39%) were released without charge and 11 (4%) faced "alternative action".
The figures also revealed that:
:: There have been 3,157 terrorism-related arrests since the September 11 attacks in the US in 2001.
:: There were 71 arrests in the last three months of December 2015 - an increase of nearly 50% compared with the previous quarter.
:: There were 143 people in custody for terrorism-related offences, with another 25 behind bars for domestic extremism or separatism.
:: More than three-quarters (78%) of those arrested were of British or British dual nationality.