Iran is stepping up efforts to target sensitive sites in Britain, including military bases, while Russia is intensifying its hybrid warfare campaign against Ukraine’s allies, the head of Britain’s domestic intelligence agency MI5 warned on Tuesday.

In his annual speech outlining the growing threats facing the UK, MI5 Director General Ken McCallum said his greatest concern over the misuse of artificial intelligence was the possibility that terrorists could use the technology to develop biological weapons or even create new pathogens.

McCallum said state-backed threats had quadrupled over the past decade, meaning MI5 was now having to devote more resources to countering them than it did during the Cold War.

On Monday (12 October), British Prime Minister Andy Burnham said Tehran was “very likely” behind a suspected plot to attack the Royal Air Force (RAF) base at Fairford, which had been used by US bombers to carry out strikes against Iran. The incident prompted a major security alert and led US President Donald Trump to withdraw American aircraft from the base.

McCallum declined to comment directly on the Fairford incident because the investigation was ongoing, but said there had been a significant shift this year in Iran’s “ambitions to attack harder targets, such as military facilities”.

“The incident at RAF Fairford … is not unique. There are other examples, not precisely in the UK but around the world,” he said.

Turning to Russia, which also denies involvement in hostile activities on British soil, the MI5 chief said Moscow remained the “number one aggressor”.

Echoing warnings from other European intelligence agencies, McCallum said Russia was employing tactics that fell short of conventional military conflict. He cited an attempted drone attack on a cargo aircraft at a German airport and a cyberattack targeting Poland’s energy infrastructure.

“It is no coincidence that Russian attackers are seeking to destabilise other European countries at a time when their military progress in Ukraine is minimal and comes at an appalling cost,” he said.