The decision not to classify Axel Rudakubana as a terrorist following the Southport murders was right because it would be unhelpful to stretch the definition of terrorism to cover all extreme violence, the UK’s terror watchdog has concluded.

Jonathan Hall KC wrote that the “legal definition of terrorism is already wide and should not be changed any further” in his post-Southport review of how extreme violence is legally classified. Expanding the definition would “increase the possibility of inaccurate use and, in theory, abuse”, he said.

Hall concluded that while “male loners, accessing violent material online, desperate for notoriety” present a real threat, terrorism must only refer to violence committed “to advance a political, religious, racial or ideological cause”, rather than serving as a label for the most serious offending.

Hall said extending the definition of terrorism would have “unintended consequences” such as hampering freedom of expression – for example, criminalising those swapping war footage – and placing pressure on resources.

“Any family member whose loved one was murdered by a violent fantasist or psychopath would have reason to ask why Counter Terrorism [Policing] and MI5 were not monitoring the individual and preventing the attack,” he said.

The review was commissioned in January by the home secretary, Yvette Cooper, to examine terror legislation “in light of modern threats we face”.

It followed a pledge by the prime minister, Keir Starmer, to update legislation to address the new threat Britain faces from “extreme violence carried out by loners, misfits, young men in their bedrooms” following the Southport murders.

Hall said that instead police should learn lessons from counter-terrorism in how to manage the risk from individuals who plan to carry out extreme violence for its own sake or because of a personal grievance.

This would include developing “a bespoke policing response” informed by the understanding that counter-terrorism police have built in recent years of how to monitor dangerous lone actors and “distinguish internet rhetoric and real-world attack planning”, Hall said.

This could pick up people such as Rudakubana, who was identified as a risk three times by the Prevent counter-terrorism programme but then dropped due to a lack of evidence of any clear extremist ideology.

Rudakubana was jailed for a minimum of 52 years for the murders of three girls and attempted murders of eight other children and two adults at a Taylor Swift-themed dance class in Southport in July last year. His attack was not considered terrorism under existing laws.

Hall felt that some counter-terrorism investigative powers, such as the ability to hold a suspect for up to 14 days pre-charge, were not “relevant to violent-obsessives”.

However he urged ministers to consider extending whole-life sentences to lone individuals who plan mass killings that are not motivated by terrorism.

It is currently not an offence to prepare for a non-terror attack, unless so many steps are taken towards carrying it out that it becomes an attempt.

“This means that no prosecution would be available if the police raided an address and found careful handwritten but uncommunicated plans for carrying out a massacre,” he wrote.

“It has become clear to me during the preparation of this report during January and February 2025 that there is a real and not theoretical gap for lone individuals who plan mass killing. If mass killing is intended, it is neither possible nor desirable to limit the offence to cases in which particularly extreme or terror-inducing forms of violence are intended.”

A government spokesperson said legislation would be amended to “close the gaps identified” in the report.

“Today’s report is an important step in that search for answers, and to tackle horrific acts driven by a fixation on extreme violence,” they said.

They added that the government would look at the report’s observation that social media was “putting long-established principles around how we communicate after an attack like this under strain” and the challenge of tackling misinformation.

A public inquiry into the Southport tragedy would be set up soon, the spokesperson said.