Islamist terrorism remains a threat to Britain 20 years after 9/11

September 15, 2021

In recent years, Al-Qaeda’s prominence as the primary perpetrator of Islamist terrorism may have been eclipsed by the Islamic State, but its network remains active and dangerous. The Taliban’s control of Afghanistan, the former base of Al-Qaeda’s core leadership, is likely to strengthen and rejuvenate the group. This recent development may also prompt a reconsideration of Al-Qaeda’s shift from large-scale plots in the West to “building and expanding its popular base in the conflicts that followed the Arab Spring”.[1]

And the Islamic State may have lost its control of territory in Syria and Iraq, but its aspiration of a revived caliphate still drives it, as well as its hatred of the west, liberal democracy, universal human-rights, and the Westphalian system of nation states. The Islamic State has inspired small cells or individuals to commit numerous terrorist acts in Britain, the rest of Europe and America, often without direct contact or operational control.

Despite their differences – for example, on the prioritisation of obtaining control of a state, or in the identification of key battlegrounds – both Al-Qaeda and the Islamic State are part of the violent Salafi-jihadi movement. This pre-dates both networks and is underpinned by an ideology that remains an allure to a small but significant number of British citizens. Evidence of this allure can be found in the statistically- supported fact that in the UK, most foiled terror plots, counter-terrorism investigations,[2] and people in custody for terrorism-connected offences are Islamist.

On the eve of the anniversary of 9/11, the director of Britain’s domestic security service, MI5, Ken McCallum, said that the threat of terrorism in the UK remains “a real and enduring thing”. He noted that MI5 has thwarted 31 “late-stage” plots to attack the UK in the past four years. Most of these, he said, were Islamist, although the number involving right wing extremists has been on the rise. Earlier, in October 2020, McCallum highlighted the increasing threat of the extreme right, but he also made it clear that “by volume … our largest threat” is “Islamist extremist terrorism”. He also noted at that time that 27 plots had been foiled, 8 of which were related to right wing extremists, the remaining 19 presumably of Islamist origin. A year prior, in October 2019, the Metropolitan Police informed the public of 24 terrorist plots foiled between April 2017 to October 2019; the majority – 16 of them – involved Islamists.

The proportion of foiled plots involving Islamists is roughly consistent with the proportion of  counter-terrorism investigations involving Islamists and the proportion of people in custody for terrorism-connected offences who are Islamists. In October 2018, Assistant Commissioner Neil Basu, the national police lead for Counter-terrorism, stated that 80% of the counter-terrorism investigations in the country – which were at a record high of 700 – were connected to the “Islamist Jihadist threat”.[3] As at June 30, 2021, there were 220 people in custody for terrorism-connected offences in Britain. As the Home Office stated, “the vast majority (70%) were categorised as holding Islamist-extremist views; a further 22% were categorised as holding Extreme Right-Wing ideologies”. On December 31, 2019, 77% of those in custody on terrorism-related offences were categorised as having “Islamist-extremist” views.[4] Nine months earlier, on March 31, 2019, the figure was slightly higher, at 79%.[5]

Some hope – or doubt regarding the seriousness of the Islamist terror threat – might arise from the significant drop in arrests in the twelve months to June this year. There were 181 arrests for terrorist-related activity in Britain, 49 less than arrests recorded in the previous twelve months, amounting to a fall of 21%. But this appears to correspond to a general reduction in crime possibly resulting from the coronavirus-related lockdowns.

Even with a general reduction of crime, however, the persistence of the terror threat did not subside during the coronavirus pandemic period. In his interview with BBC Radio 4’s Today, the head of MI5 stated, “Even during the pandemic period which we have all been enduring for the past two years, we have had to disrupt six late-stage attack plots”. McCallum warned the British public, “the terrorist threat to the UK, I am sorry to say, is a real and enduring thing”. That the majority of these plots is Islamist-related should encourage a greater understanding of Islamism; who its key players are; what they believe, value, and seek to achieve; what their methods are; how successful they are; and what can be done to meet the challenge they pose. These lines of inquiry are precisely what guide Policy Exchange’s Understanding Islamism project, launched in 2020.

Author bio

Dr Damon Perry is a Senior Research Fellow at Policy Exchange. He received his PhD from the Department of War Studies, King’s College London, in 2016. He is the author of The Global Muslim Brotherhood in Britain: Non-Violent Extremism and the Battle of Ideas, published in 2018 by Routledge. In 2019, whilst an Associate Research Fellow at the International Centre for the Study of Radicalisation (ICSR), London, Dr Perry was commissioned by the Commission for Countering Extremism to publish an academic paper on mainstream Islamism. His most recent publication is the report The Islamic Movement in Britain, published by ICSR in 2020.

[1] Katherine Zimmerman, “Al-Qaeda After the Arab Spring: A Decade of Expansion, Losses, and Evolution”, Current Trends in Islamist Ideology, April 6, 2021,

[2] “Home Affairs Committee Oral evidence: Counter-terrorism”, HC 750, House of Commons website, October 24, 2018, Q.54-55,

[3] “Home Affairs Committee Oral evidence: Counter-terrorism”, HC 750, House of Commons website, October 24, 2018, Q.54-55.

[4] Home Office, “Operation of police powers under the Terrorism Act 2000 and subsequent legislation: Arrests, outcomes, and stop and search Great Britain, year ending December 2019”, March 5, 2020, p.17. Available at

[5] Grahame Allen and Esme Kirk-Wade, “Terrorism in Great Britain: the statistics”, House of Commons Library Briefing Paper, Number CBP7613, March 26, 2020, p.22. Available at


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