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The number of people arrested for terrorism-related offences has reached record levels, new figures reveal.

In the year to March, 299 terror suspects were detained - an increase of 31% on the previous year - of which 100 were charged with a terror-related offence, Home Office figures show.

It is the highest number since officials began collecting data in September 2001.

The previous peak of 284 occurred in 2005, the year of the 7 July attacks.

Among those arrested, there was a "marked increase" in the number who considered themselves to be of British or British dual nationality, officials said.

In 2014/15, they accounted for more than three-quarters of those detained for terrorism-related offences, compared with 52% in the year to March 2011.

Image copyright AP Image caption There was a spike in the number of terror arrests at various points, including after the 9/11 attacks

The number of 18 to 20-year-olds arrested more than doubled on the previous year from 20 to 43, the report found.

The figures show a spike in the last three months of last year, when there were 106 arrests.

Analysis: BBC home affairs correspondent Dominic Casciani

Syria has changed everything. When the jihadists began moving into Syria - and their would-be recruits began arriving from the West - the arrests began to rise.

Just over 18 months ago, the Crown Prosecution Service made clear that anyone joining Syria's conflict risked prosecution because the UK's definition of terrorism includes acts of violence committed overseas. And the figures have shown how that policy has since been pursued.

Read Dominic's full post here

The rate fell from January to March this year, with 67 terror-related arrests - but this was still higher than the same period in the previous two years.

A Home Office statistical bulletin setting out the data said that there had been fluctuations in the number of terrorism-related arrests since the attacks on the World Trade Centre on 11 September 2001.

There were spikes in the number of arrests after 9/11, around the time of the beginning of the US-led invasion of Afghanistan, and immediately after the 7 July London bombings.

"Soon after this, the number of terrorism-related arrests declined, until late 2010," it said.

"In late 2010, the Arab Springs began, and throughout the years since the initial uprising, the number of terrorism-related arrests in Great Britain has seen a steady rise."

Female suspects

In 2014/15, there were 35 women arrested on terror-related offences; also a record figure and more than treble the number five years ago. Eight of those arrested were under 18.

There has also been a significant increase in the number of suspects arrested who were aged 30 and over, with a rise of more than a third compared to the previous year.

Of the 299 people arrested in 2014/15, fewer than half - or 100 - were ultimately charged with terror-related offences.

The Home Office said this was the highest proportion since records started, "suggesting that police were more frequently able to find evidence to support the link to terrorism following a terrorism-related arrest".

The total number of terror arrests in the UK since recording began 14 years ago is just under 3,000.

Last month Mark Rowley, the country's leading counter-terrorism officer, disclosed that suspects are now being held at a rate of more than one per day.