Dr Paul Gill, an academic who has studied over 100 “lone actor” terrorists, issued the stark warning after police said they believed the 29-year-old man who allegedly staged a terrorist attack at Leytonstone tube station on Saturday evening was acting alone.

Gill, a lecturer in security and crime science at University College London who has worked with US counter-terrorism officials, said: “It is very low-tech, low-capability and hard to detect ahead of time. Shouting ‘This is for Syria’, stabbing people is worrying as it is easy to do.”

Online jihadi propaganda, most prominently in Inspire magazine, has for years urged extremists to carry out whatever attacks they can, no matter how low-tech.

Gill said: “The thing to remember is that no matter how crazy and illogical a single act of violence appears at first glance, there is usually some rationality on the offenders’ half. At the very basic level, they are trying to effect some form of political change. Some perpetrators believe that this can only be achieved by killing as many people as possible.”

In the Leytonstone station attack, the suspect was allegedly shouting about Syria, which the UK House of Commons this week authorised British forces to bomb to try to tackle the Islamic State terrorist group.

Gill’s work included a study for the US Department of Homeland Security, in which 119 lone actor terrorists were examined. Lone actors carry out attacks not just in the name of Islamism, but also influenced by extreme rightwing ideology as well as anti-abortion views, and environmentalism.

Research by Gill and other academics found there may be clues ahead of an attack by a single individual. It says: “For a large majority (83%) of offenders, others were aware of the grievances that later spurred their terrorist plots or actions. In a similar number of cases (79%), others were aware of the individual’s commitment to a specific extremist ideology.”

So-called lone wolves are not just driven to violence by an ideological cause, said Gill, who added: “One-third had have mental health problems and others had other stressors such as having lost their job. The ideology gives them a buffer from their other problems.”

Talking about the Leytonstone attack, the academic said: ”Was this a vulnerable person, who was going to act violently anyway?”

Lone actors are those outside of a terrorist network, and the UK has seen such attacks before. Roshonara Choudhry tried to assassinate the Labour MP Stephen Timms in 2010 as punishment for his support for the Iraq war. She radicalised herself and wanted to die as a martyr after watching more than 100 hours of video sermons from the extremist cleric Anwar al-Awlaki that she had found surfing the internet. Previously she had been a gifted student with no sign of criminality or extremism.

Britain’s terrorist threat level remained unchanged on Sunday after the attack at Leytonstone underground station. It has been at severe since 2014, meaning an attack is “highly likely”. The next level – the highest – would mean counter-terrorism analysts believe an attack is imminent.

The biggest threat comes from Isis, which has proven capable of inspiring or staging attacks around the world. After the Paris gun and bomb attacks three weeks ago, which killed 130 people, UK officials feared a new chapter in terrorist tactics.

Isis propaganda has led officials to fear lone-wolf attacks, possibly leading to small levels of death or injury, but the multiple and near-simultaneous Paris attacks resulted from large-scale planning designed to execute a terrorist spectacular.

After Paris, security officials in western countries that fear attack by Isis or its followers, including the US and UK, reviewed terrorism suspects to see if they had underestimated the level of danger they pose.

Because there are more suspects than resources to fully monitor them, security agencies rank them according to the danger they are feared to pose and then deploy assets accordingly. The most dangerous will be monitored 24/7.

Source: Guardian Newspaper, UK