Twenty-five years after the September 11 attacks transformed global security policy, Britain’s intelligence chief has warned that future attacks may not resemble the threats authorities have spent decades preparing to confront.
MI5 Director General Ken McCallum said security agencies must avoid becoming too focused on past terrorist attacks and familiar methods. He cautioned that the next major strategic shock could already be developing in an area that governments and intelligence agencies are not currently watching closely enough.
McCallum’s warning comes as governments mark the 25th anniversary of the 9/11 attacks, which killed nearly 3,000 people and fundamentally changed international counterterrorism efforts.
Future Threats May Look Very Different From 9/11
McCallum said one of the most important lessons from September 11 is that the next major security crisis is unlikely to copy the previous one.
Rather than preparing exclusively for the tactics and targets associated with earlier terrorist attacks, intelligence agencies need to anticipate threats that could emerge in completely different forms.
Al Qaeda has been significantly weakened since 2001, but McCallum said the ambition among extremist organizations to conduct mass-casualty attacks remains. He pointed to a recently disrupted Islamist plot in Manchester as evidence that large-scale terrorist ambitions have not disappeared.
The warning highlights the difficulty facing intelligence agencies: focusing too heavily on known threats can create blind spots when adversaries change their methods, targets or technologies.
Terrorism Now Shares the Threat Landscape With Cyberattacks and Sabotage
McCallum also emphasized that terrorism is no longer the only major security challenge facing Britain.
MI5 is increasingly dealing with state-backed activity, including sabotage conducted through criminal proxies and cyberattacks targeting critical infrastructure such as power facilities. The agency has previously warned that hostile states are increasingly using covert and deniable methods to disrupt the UK.
The changing threat environment means national security can no longer be treated solely as the responsibility of intelligence agencies. Many essential systems and services are operated by private companies, making cooperation between government, businesses and academic institutions increasingly important.
McCallum argued that organizations must know in advance who controls critical systems, who has the authority to respond during a crisis and how information will be shared.
MI5 Calls for Greater Preparation and Resilience
The intelligence chief’s message on the 25th anniversary of 9/11 was ultimately a call for greater preparedness rather than a prediction of a specific future attack.
He stressed that authorities need to remain flexible and willing to adapt as threats evolve. That includes recognizing emerging risks before they develop into major security crises and strengthening cooperation across different sectors.
The warning comes amid a broader shift in the UK’s national security priorities, with MI5 facing both persistent terrorism investigations and a growing number of state-threat cases. The agency has previously said it has disrupted numerous late-stage terrorist plots since 2020 while also expanding its focus on hostile state activity.
For governments around the world, the anniversary of 9/11 therefore carries a message beyond remembrance: preparing for the next major crisis requires anticipating threats that may not yet fit the patterns of the past.
