Terrorists could exploit artificial intelligence to target Britain with drones or biological weapons, the head of MI5 has warned.

Speaking after his annual speech at MI5 headquarters in London, Sir Ken McCallum said the UK had entered a “new era of national security” and the security service was directing more resources to keeping Britain safe now than in the Cold War, warning that essential services such as banking, flights, and healthcare were at risk of being disrupted by adversaries, including Iran and Russia.

He warned about the growing threat of AI provoking real fear that terrorists could use the technology for warfare, saying “we’ve caught terrorists seeking to exploit AI to improve their reconnaissance and attack methodologies”.

He said the possibility of AI-enabled drones added “a new twist” for bad actors and warned the greatest concern is “AI’s potential to change the stakes on existing or even new bioweapons”.

“These risks are real. The UK Intelligence Community – MI5, GCHQ, MI6 – is working closely with the UK’s globally respected AI security institute to take them on. Part of that means retaining the capability edge against those who mean the UK harm. As they seek to harness AI, we must stay ahead, so these powerful technologies bolster rather than undermine our shared security,” he said.

Putting the public on guard, Sir Ken warned: “We have again entered a new era of national security”.

He called for a “whole-of-society effort” to face threats to national infrastructure, warning that hacks could disable people’s banking services, drones could disrupt flights, and cyber-attacks on hospitals could impact health treatment.

The MI5 director general also said that the suspected terror plot against RAF Fairford in Gloucestershire, which prime minister Andy Burnham said was “almost certainly” directed by Iran’s Islamic Revolutionary Guard, was “not unique in the UK”, with Iranians seeking to expand their hybrid campaign against Britain this year.

In the past twelve months, MI5 investigations have led to more than 50 arrests in Iran-linked operations in the UK, and its state threats caseload has quadrupled in the past decade, he said.

Sir Ken added: “You might be surprised to know that in 2026, MI5 is devoting more resource to countering state threats than during the Cold War.”

He said that there have been dozens of arrests under the National Security Act in the three years since it came into force, with cases linked to Russia, Iran and China.

“Anyone tempted by apparently easy cash from shady overseas taskmasters might want to bear this in mind,” Sir Ken warned.

He said that Russia remains “aggressor number one”, with Russian military and intelligence services “once again escalating their attempts at hybrid warfare”, citing a cyber-attack on Polish energy infrastructure and an attempt to use a drone to blow up a cargo plane in Germany.

Sir Ken also called out Iranian use of “criminal proxies to try and intimidate oppositionists, Iranian media organisations and Israeli sites”.

His warning comes after he revealed Britain faces greater and more complex terror threats now than on 9/11, in an exclusive interview with The Independent last month.

Addressing journalists after his speech on Tuesday, Sir Ken said: “The Iranians in the UK are principally using a modus operandi of hiring criminals to do their biding. Their level of capability is really a function of the sophistication level of those criminals”. But he warned that the UK should be readying itself for more aggressive plots from the Iranian security services.

Speaking about the ongoing threats from terrorism, Sir Ken said that MI5 is still having to respond to attempts from radicalised Islamists to carry out mass casualty attacks in the UK. And an increase in extreme right-wing terrorism, with a growing number of cases where “extremist versions of anti-immigration and anti-Muslim grievance are tipping into terrorist intent”.

He cited a case where, a few months ago, MI5 was investigating a radicalised extreme right-wing 13 year old in the UK. This investigation “generated insight that enabled one of our international partners to prevent a lethal attack on their soil”, Sir Ken said.

Sir Ken also announced that MI5 has launched an AI Threat Assessment Centre (AITAC) this year, which will produce assessments of the risks posed by the new technology.

Speaking to journalists after his speech, Sir Ken added: “In the case of bioweapons…one concern would be that comparatively low sophistication actors may have a capability uplift in the AI era, if the guard rails don’t operate or do not function as intended.”

Sir Ken explained: “It has long been the case that many terrorists would dearly love to have some kind of capability around chemical or biological weaponry, but that hasn’t been easy for them to achieve. One risk, and as I said in my speech this is not yet manifest, but one risk is that AI could enable knowledge to get into the hands of people we would not want to have that knowledge.

“A second additional risk, much discussed…is the possibility that AI could generate novel pathogens not previously seen, so these are among the risks that we are seeking to address.”

Asked whether Britain will be able to get back to a less fractious time, Sir Ken said: “Our planning assumption is not that this is a temporary blip, and we will all be back to normal by next Christmas.

“We are planning on the basis that, in effect, the period of comparative geopolitical stability following the end of the Cold War has sadly ended and we are back in a more contested era now. We are planning on the basis that these risks will endure.”