The number of suspect terrorists arrested by police has dropped 20% in the last year, figures show.

There were 259 people detained for terrorism-related activity in the year ending September 30, compared with the 325 arrests in the same period in 2018, according to the Home Office.

Of these, 96 (37%) were released on bail or released under investigation – meaning they were not subjected to any restrictions while enquiries into the offences continued.

There were 88 (34%) charged and 62 of these were for terrorism-related offences.

A further 14 (5%) received a caution, were recalled to prison or handed over to immigration authorities and 60 suspects (23%) were released without charge.

During the same period 53 terrorists were released from prison, the data report showed.

The news comes less than a week after the London Bridge terror attack which claimed the lives of Saskia Jones and Jack Merritt.

Convicted terrorist Usman Khan embarked on a killing spree while attending a prisoner rehabilitation programme at Fishmongers’ Hall last Friday afternoon.

The 28-year-old, armed with two knives and wearing a fake suicide vest, was tackled by members of the public, including ex-offenders from the conference, before he was shot dead by police.

Usman Khan
Usman Khan was released from prison on licence in December 2018 (West Midlands Police/PA)

Khan, a British national from Staffordshire, was released from prison on licence in December 2018, halfway through a 16-year prison sentence, after he was convicted of terror offences in February 2012.

He was part of an al Qaida-inspired terror group – linked to radical preacher Anjem Choudary – that plotted to bomb the London Stock Exchange and build a terrorist training camp on land in Pakistan-controlled Kashmir owned by his family.

A list of other potential targets included the names and addresses of the Dean of St Paul’s Cathedral in London, then London mayor Boris Johnson, two rabbis, and the American Embassy in London.

Since his release he was one of about 3,000 live subjects of interest being monitored by MI5, but all convicted freed offenders are the focus of lower level investigations, the PA news agency understands.

It is understood a risk assessment was carried out by police and probation officers on Khan’s latest trip to London and attendance at the event, as would be standard practice with all prisoners and offenders on licence in such circumstances.

Police and probation staff would have been at the event.

The Ministry of Justice (MoJ), which was involved in the event organised by the University of Cambridge and the Learning Together programme, said it could not comment on the risk assessment while the police investigation into the incident continued.

The latest attack, which took place just weeks after the terror threat level was lowered from severe to substantial, prompted concerns over the length of sentences terrorists faced in prisons and the conditions they were subjected to on release.

As a result, the Government has launched an urgent review of currently serving prisoners at risk of radicalisation, as well as convicted offenders who have since been released from jail.

Incident on London Bridge
Tributes to Jack Merritt and Saskia Jones on London Bridge (Rick Findler/PA)

Police, security services and probation teams are examining the files of about 200 known extremists, with some reportedly facing bans from large towns and cities.

About 70 of the cases relate to convicted terrorists freed on licence before the end of their sentences.

The files of another 150 are said to also be on the list as part of the review, including inmates approaching release and suspects who were arrested under terrorism laws but later convicted of lesser offences and are now free.

The latest Home Office figures showed 15 of the 53 terrorists released from custody in the last year were given sentences of less than four years.

The most common sentence was less than four years, accounting for 43% of sentences (19 out of 44 convictions).

Just one offender was handed a life sentence, down from seven in the previous year.

The number of sentences of 10 years or more also fell, from eight to five compared with last year.

Non-custodial sentences also fell from 10 to one in the latest year.

Overall there were 224 people held in custody for terrorism-related offences in the country in the year to the end of September.

The “vast majority” (77%) were described as holding Islamist-extremist views, the data report said.

A further 17% were categorised as holding far right-wing ideologies.

Since September 11 2001, 3,769 people have been arrested for terrorist-related activity. Some 61% of these (2,781) said they were British or had a dual nationality.

MI5 has about 600 live investigations at any one time, and since the Westminster terror attack in March 2017, 25 plots have been thwarted by police and security services.