MI5 chief warns UK faces ‘worst of both worlds’ 25 years on from 9/11

Britain faces the “worst of both worlds” as hostile states pose a growing security threat while terrorism persists, the head of MI5 has warned on the 25th anniversary of the September 11 attacks.

Sir Ken McCallum, director general of the Security Service, said the threat landscape had changed significantly since 2001 and called for Britain to continually adapt its national security defences.

Writing in The Independent on the anniversary of the attacks, McCallum described the threats facing the UK today as “markedly different” and called for “relentless adaptation”. He said security should be treated as a “shared national endeavour”.

“Sadly, mass-casualty terrorist ambition endures… but the terrorist threat now sits alongside strategic national security threats posed by capable states,” he wrote.

McCallum used an analogy first made by former CIA director James Woolsey after the end of the Cold War to describe the challenge.

“In the aftermath of the Cold War, CIA director James Woolsey spoke of the West having ‘slain a large dragon’ but facing a ‘bewildering variety of poisonous snakes’,” he said.

“With a nod to David Kilcullen, we now face the worst of both worlds: dragons are back, but snakes persist.”

Counterinsurgency expert David Kilcullen later developed the analogy in The Dragons and the Snakes: How the Rest Learned to Fight the West, examining threats posed to Western powers by state adversaries and non-state groups.

McCallum said the international campaign against al-Qaeda following the September 11 attacks had significantly reduced the organisation’s capabilities.

He said: “Al Qaeda had to be not just taken on, but taken down. A gargantuan multinational effort, powerfully spearheaded by the US, devised new capabilities to dismantle the core of the organisation in Pakistan’s federally administered tribal areas, into which it had been pushed by the Afghan campaign.

“It worked. Al Qaeda remains a threat today, but its capabilities are a fraction of 2001’s. That rolling back was not inevitable; it was forced.”

However, McCallum warned that security agencies could not rely on measures developed to counter previous threats.

“We must resist the temptation to admire the defences we built yesterday and instead build the ones we will need tomorrow,” he warned.

The MI5 chief described foreign policy as “harder than many commentators allow”, while avoiding comment on individual diplomatic issues.

He warned that Britain must contend with hostile state activity conducted below the threshold of conventional warfare, including sabotage, political interference and cyber attacks.

McCallum said: “Contending with rising State-backed aggression – whether sabotage subcontracted to criminals, or covert interference in our democracy, or destructive cyber attacks on power stations – demands new laws as well as new tradecraft.

“We cannot wait for the next shock to discover who owns the vulnerability, who has the authority to act, or who was supposed to pick up the phone.”

McCallum did not identify individual states in the article.

He pointed to recent attacks on synagogues when discussing British “assets” requiring protection and warned that responsibility for protecting important infrastructure increasingly extended beyond government.

“In 2026, unlike 2001, many of the assets, systems and services under threat sit in private sector hands. This means many of the most critical decisions will be taken not in COBR but in boardrooms,” he added.

The changing ownership of infrastructure means government, businesses and other organisations need to work more closely to identify vulnerabilities and respond to security incidents.

“We need a new team of teams, preserving an open economy but cooperating across government, industry and academia, to close vulnerabilities and enable swift coherent action when crises hit.”

McCallum issued what he described as a “call to arms” for organisations and individuals outside the intelligence services to play a greater role in protecting national security.

“This is my call to arms after 25 years: government, business, academia, and the public must treat national security not as the specialist concern of a handful of agencies, but as a shared national endeavour,” he said.

McCallum, who became director general of MI5 in 2020, said the victims of the September 11 attacks were owed “preparation, resilience and the courage to adapt”.

“The horrors of 9/11 will never leave me. What sits with me every day, 25 years on, is MI5’s perpetual responsibility to keep adapting, at even greater pace, as we seek to deepen the UK’s resilience – now to both dragons and snakes.”