The number of people being arrested for terror offences in the UK has hit a new record, with 412 arrests in 2017 as the threat continues to rise.
The figure rose by more than 58 per cent on the previous year, with the period seeing 36 victims killed and hundreds injured in the Westminster, Manchester, London Bridge and Finsbury Park attacks.
Only a third of the arrests resulted in a criminal charge, and not all for terror-related offences, with some people released without further action, on bail or under alternative measures.
The vast majority of suspects were men, who were mainly British and of Asian appearance, although the number of white people arrested rocketed by 61 per cent to make up more than a third of the total.
Ben Wallace, the security minister, said the rise in arrests was “testament to the breadth of work undertaken by the police, security services and wider judicial system in identifying and stopping terrorism in our communities and bringing those responsible to justice”.
“The police and security services have been clear about the scale of the threat we face,” he added.
“We will continue to work with them and other agencies to ensure we have a broad response to all forms of terrorism both now and in the future.
“The public should remain alert but not alarmed and report any suspicions they have about unusual activity or behaviour to the appropriate authorities.”
There were 86 terror trials in 2017 and 90 per cent resulted in a conviction, as defendants were only acquitted in eight cases, according to Home Office figures.
By the end of the year, there were 224 terrorist prisoners in the UK, up a quarter on 2016, and the number is set to rise.
The vast majority, 86 per cent, held Islamist extremist views, 9 per cent were affiliated to the far right and 5 per cent had other ideologies.
Part of the increase in arrests was accounted for by large-scale police operations in the wake of five terror attacks.
A dozen people were arrested in connection with the Westminster attack in March, 23 over the Manchester Arena bombing, 21 following the van-and-knife rampage in London Bridge, one in Finsbury Park and seven linked to the Parsons Green explosion.
All suspects were later released without charge, with the exception of the Finsbury Park attacker and alleged Parsons Green bomber, and a review revealed that security services could have prevented the Manchester and London Bridge attacks.
Darren Osborne was jailed for life last month for ramming a van into Muslim worshippers in London, in perceived revenge for Isis-inspired terror attacks and grooming gang activity in Rotherham.
Ahmed Hasan, an 18-year-old Iraqi asylum seeker, denied carrying out the Parsons Green attack and is currently on trial at the Old Bailey.
Police have used a variety of legal powers to investigate terror suspects, including 767 stop and searches under the Terrorism Act – which resulted in 61 arrests – and more than 16,000 Schedule 7 checks at land, sea and airports.
The latest figures were released after officials revealed that 10 Islamist and four far-right terror plots have been foiled since the Westminster attack in March 2017.
Mark Rowley, the outgoing head of national counter-terror policing, made the figure public for the first time to “illustrate the growth of right-wing terrorism”.
“The right-wing terrorist threat is more significant and more challenging than perhaps the public debate gives it credit for,” he added.
Security services have described the current threat facing the UK as “unprecedented”, with the current level set as severe – meaning further attacks are considered highly likely.
Police and MI5 are running more than 600 live counter-terror investigations relating to 3,000 individuals.
There is a wider pool of 20,000 former “subjects of interest” who have previously featured in probes and who are kept under review.
While the bulk of the threat emanates from Isis and its supporters, the far right is gaining recruits by perpetuating the idea of a cultural “war against Islam” and radicalisation is increasing on both sides.
Last week, an Isis fanatic who tried to groom a child “death squad” for simultaneous terror attacks across London was convicted, followed by an autistic teenager who planned a car-and-knife massacre in Cardiff after watching propaganda videos online.
A growing number of attacks have been launched or planned by the far right, including a man who attempted to murder a Muslim woman and 12-year-old girl in “revenge” for the 7/7 bombings and Parsons Green terror attacks.
Several members of the neo-Nazi terrorist group National Action have been arrested since it was proscribed in December 2016, and one of its supporters was jailed for planning a knife attack at a gay pride event in Cumbria.
The rise in extremism has driven global action to counter the spread of terrorist propaganda and hate speech online, as well as proposals for tougher jail sentences for terror offences.
But the Parole Board warned that radicalisation in prison was widespread and increasing penalties for less serious offenders – like those found guilty of spreading terrorist material online – could “result in them becoming more likely to commit terrorist acts when they are released”.
Specific terror offences are mostly contained in the Terrorism Acts of 2000 and 2006, which were drawn up to outlaw behaviour that skirted the boundaries of pre-existing legislation, and are mostly used in cases where a common law offence has not been committed.
Terrorists who have committed murder or other serious crimes, like Osborne and the murderers of Lee Rigby and Jo Cox, are therefore not charged with terrorist crimes.
The acts formalised the definition of terrorism and introduced powers of arrest without warrant for suspects, and stop and search without prior suspicion.
They created new crimes that made it illegal to collect or possess “information of a kind likely to be useful to a person committing or preparing an act of terrorism”, glorify or encourage terror attacks and disseminate terrorist publications.
The offence of “preparation of terrorist acts” that was introduced by the Terrorism Act 2006 has been prolifically used to jail people attempting to join Isis in Syria and Iraq, or mount plots at home, and can be punished with life imprisonment.