The Manchester attack was therefore inconsistent with the perceived trend towards low complexity attacks, and the marauding vehicle and bladed attacks in London Bridge in June seemingly confirmed the use of an IED in Manchester as anomalous. However, on 15 September, an IED partially detonated on a tube train at Parsons Green station. The attack shared some similarities with the one in Manchester six months earlier; crowded places were targeted, Triacetone Triperoxide (TATP) manufactured from legally available materials was used in both devices and the bombers, both British residents with immigrant backgrounds, were known to police and MI5. In both instances, the UK threat level was raised to CRITICAL while MI5 and the police sought to identify suspects in the attack and negate the risk of further devices being used in attacks.
The successful use of IEDs in two Islamist attacks within six months of each other potentially signalled an increase in the capability of terrorists operating in the UK. Both Salman Abedi and Ahmed Hassan (responsible for the Manchester and Parsons Green attacks respectively) displayed the ability to construct explosive devices using commercially available materials, and to deploy those devices without being detected. Abedi also conducted pre-attack reconnaissance and identified key vulnerabilities of public venues like Manchester Arena; the appearance of largely unprotected crowds at a predictable time and place. This suggests that Abedi may have received training or support from an overseas third party, or utilised instructional manuals available online. Hassan was able to construct a viable device, although the timing of his attack appears premature considering the construction of it and its ultimate failure to successfully detonate.
Terrorist attack plans, including those involving explosives, are frequently disrupted. The success of Abedi and Hassan is more likely attributable to MI5 and police currently operating at capacity due to the heighten threat environment, rather than to an increase in the sophistication of threat actors. However, it is significant that both Abedi and Hassan were domestic actors; Abedi was a British citizen, and Hassan had resided in the UK since 2015 and is not known to have been affiliated with international terror groups. In contrast, earlier Islamist attacks in Europe which have involved explosives were conducted by a cell with links to Daeshs external operations unit. This could indicate an increased willingness on the part of inspired actors to undertake more complex attacks using IEDs. Regardless, successful attacks will contribute to the motivation of aspiring extremists.
The attacks in Manchester and London highlight the relative ease with which extremists in the UK can construct viable IEDs utilising commercially available ingredients and components. Making this acquisition more difficult should be a priority for suppliers in the commercial chain, along with police and MI5 exploiting opportunities online to disrupt such attack plots. Businesses should be aware of the increasingly diverse methodologies employed by UK terrorists, and take appropriate action to harden their premises and prepare their employees for such an eventuality. Additionally post-incident responses to the use or suspected use of explosives by terrorists frequently involve comprehensive cordons which can result in significant business interruption for businesses located near the scene, in addition to the expected property damage from explosions.
Successful attacks are likely to contribute to the motivation of aspiring extremists to undertake further attacks. Should the step-change in terror threat seen this year be indicative of the likely frequency of attacks in the next twelve months, further use of IEDs against similar targets is probable. Those attacks are likely to be Islamist extremist in nature, the IEDs made from commercially available materials and used against a range of targets including crowded places, transport hubs and iconic sites. The possibility of the IEDs having timers, rather than utilised as part of a martyrdom operation, is indicative of a sustained insurgency tactic and campaign rather than isolated attacks.