Since the emergence in 2013 of the Islamic State of Syria and al-Sham, later Islamic State (IS), followed by its declaration of a caliphate, the British government has estimated that over 850 British citizens and residents travelled to join the group in Iraq and Syria.  Of these, it said that 400 had returned to the United Kingdom (UK), and around 15 percent, or about 120, had been killed. The remainder—around 300 individuals—are still active in Iraq and Syria, or are in neighboring countries such as Turkey. The director general of MI5, the UK’s internal security service, said in October 2017 that to contain this threat, the intelligence services were operating at a scale “greater than ever before,” including running 500 “live operations” and monitoring 3,000 individuals “engaged in extremist activity.”  The authorities have disrupted 13 attacks since June 2013 (BBC, March 6). Nonetheless, since then, jihadists have carried out three significant attacks in the UK, killing 31 people.
Militants Abroad and Attacks at Home
British jihadists played a minor role in supporting IS’ forerunner, al-Qaeda in Iraq, in the mid-2000s. IS, however, attracted significant numbers of UK nationals after its capture of Raqqa and Mosul, in January and June 2014 respectively, and its subsequent declaration of a caliphate. The large number of recruits was catalyzed by a number of factors, such as a desire to “protect” Sunnis against the Iran-backed governments of Iraq and Syria, or an attempt to fulfill various emotional and psychological needs and achieve a sense of belonging. Above all, however, recruits appear to have been attracted to the idea of an “Islamic State” and its enforcement of sharia. For instance, Tareena Shakil, a healthcare worker who was convicted in 2016 of joining IS, told the court that she travelled to join the group because she wanted to live “under sharia law,” and that her decision was “not about fighting or killing anybody” (BBC, January 21, 2016). Indeed, the caliphate’s primary attraction for UK recruits is mainly ideological; aside from a desire to live under hardline Islamic law, recruits have very little in common in terms of age, education and other socio-economic factors.
Since IS’ declaration of the caliphate, attacks in the UK have included using a vehicle to mow down pedestrians in Westminster, carried out by an individual apparently inspired by IS; a vehicle and knife attack near London Bridge by three individuals again inspired by IS; and a bomb attack in Manchester by a lone individual, who seems likely to have received specific bomb-making training from militants in Libya shortly beforehand. Significantly, all three individuals had substantial prior exposure to British radical networks; respectively in radical mosques in Luton, a hotbed of hardline Salafism, through the pro-jihadist al-Muhajiroun network in London, and through family links to the Libyan Islamic Fighting Group (LIFG), a defunct organization formerly aligned with al-Qaeda.
Notably, however, aside from the Manchester bomber’s trip to Libya, none of these individuals had spent time in Iraq or Syria, and little evidence of direct contact with jihadists inside the IS caliphate has yet surfaced. Although, evidence of such links may still emerge in due course. However, some other attempted attacks show more direct links with IS-held territory. For instance, in September 2017, an 18-year-old Iraqi asylum seeker attempted to set off a homemade bomb on a metro train, although the device exploded at Parsons Green station without causing any fatalities. This individual had received training prior to arriving in the UK in October 2015. Although he denies the charges against him, from an earlier interview it appears this may have been conventional military training (BBC, March 17). However, there is no evidence that IS directly assisted with his attack.
In addition, there is no evidence that any of the 13 disrupted plots (referenced above) were directed by IS central leadership. Therefore, this would seem to suggest that IS’ leadership has not significantly prioritized attacks in the UK, in contrast to its clear involvement in planning the November 2015 Paris and July 2016 Nice attacks. Given the sheer number of IS sympathizers in the UK and the large number of British citizens fighting with the group, this would appear to be a deliberate decision. Perhaps this reflects that the UK—due to its geography, strong security services and strict controls on guns and explosive purchases—is seen by the group as a relatively challenging and therefore less attractive target.
The Returnee Threat
However, even if IS’ leaders have not prioritized attacks in the UK, the large numbers of returnees seems likely to increase the threat in the longer term. No public information is available on what proportion of returnees continue to support IS. Many are likely to be, to some extent, disillusioned with the group or fearful of what might happened to them if they had remained in Iraq or Syria. By contrast, those who have remained in these areas are likely to be the most ideologically committed and, given their involvement in atrocities, those who have the most to fear from returning home. It is notable that Alexanda Kotey and El Shafee Elsheikh, two of four British jihadists known as “The Beatles,” who were prominently involved in the torture and killing of Western hostages, were captured in February by Kurdish forces in Syria—they do not appear to have been attempting to return to the UK. Rather, some reports suggested they were seeking to cross into Turkey.
A gray area likely exists in which many returnees are disillusioned by aspects of IS, but remain supportive of some of the group’s principles and actions, like its commitment to creating an Islamic State and enforcing sharia. Indeed, it is notable that no British IS returnees have publicly spoken out against the group, even though that would likely lead the authorities to take a more lenient approach toward them. While such silence may be motivated by fear, it may also suggest continuing sympathy. It is possible that IS—or successor jihadist groups—may yet be able to weaponize such latent sympathies, whether through propaganda, or by reaching out to them directly through informal networks of international IS veterans, which are likely to persist for decades.
The lack of IS returnee attacks to date may also reflect that the group’s propaganda networks remain disrupted. For instance, the monthly English-language online magazine Rumiyah has not been published since September. This occurred shortly before the group lost Raqqa, one of its last major cities and a hub for foreigner-led propaganda efforts. It is therefore possible that if the group re-invigorates its propaganda activities—and particularly if it succeeds in forming a coherent narrative for its losses—it will succeed in catalyzing the large returnee population, especially if it successfully portrays its rule as a golden era and blames the West for the failure of its governance project.
The threat of increased returnee attacks, potentially with greater direct IS input, may be compounded by government uncertainty over how to deal with the issue. For instance, Rory Stewart, a junior but influential Foreign Office minister, claims “the only way of dealing with them will be, in almost every case, to kill them” (BBC, October 23, 2017). Meanwhile, the government has removed citizenship from at least 200 foreign fighters, in an attempt to stop them from returning (The Times, February 17). This, however, could have complex repercussions, for instance through perpetuating an aggrieved UK foreign fighter population abroad that may be increasingly motivated to organize strikes at home.
In contrast to this tough approach abroad, the treatment of many returnees has been exceedingly lenient, with only a fraction of returnees prosecuted. Indeed, a recent parliamentary report on terrorist sentencing recommended that—such was the level of prison radicalization and that absence of an effective de-radicalization scheme—those convicted of more minor terrorism offensives should receive a non-custodial sentence.
Other trends also exist that could trigger an increase in IS violence in the UK, including by IS veterans and returnees. If IS continues building its presence in Afghanistan and Pakistan, including in Kashmir, the group will have increased access to British Muslim communities, nearly half of which derive from Pakistan and Afghanistan. Similarly, IS’ efforts to establish itself in Somalia, where it is in direct competition with the well-established al-Qaeda-aligned al-Shabaab group, could also give it increased reach into British-Somali communities. Many in these communities are from Puntland, where IS has achieved some success at the hands of Abdul Qadir Mumin, who himself lived in the UK in the mid-2000s (see Militant Leadership Monitor, October 5, 2016). Due to these factors, although returnees have played a limited role in IS-linked violence in the UK to date, there is clear potential for these veterans to play an increased role in UK terrorism in the years ahead.
 Parliament, “British Nationals Abroad: Middle East: Written question – 127983”, February 19, 2018 http://www.parliament.uk/business/publications/written-questions-answers-statements/written-question/Commons/2018-02-19/127983
 Transcript of Andrew Parker speech, October 17, 2017, MI5.gov.uk (https://www.mi5.gov.uk/who-we-are-video-transcript)
 UK Parliament, “Letter from the Chair of the Justice Committee to the Chairman of the Sentencing Council, dated 24 January 2018” https://publications.parliament.uk/pa/cm201719/cmselect/cmjust/746/74604.htm