Russia’s intelligence service has been intent on causing “mayhem” in the UK because of London’s support for Ukraine, the chief of Britain’s domestic intelligence service said on Tuesday.

Ken McCallum also said MI5 had responded to 20 Iran-backed plots since January 2022 that presented potentially lethal threats to British citizens and UK residents.

Russia and Iran had turned to employing criminals and private intelligence officers to do their work on British soil, he said.

From Russia, Britain should “expect to see continued acts of aggression here at home” with its military intelligence agency the GRU on “sustained missions to generate mayhem” on the country’s streets, McCallum said.

“We’ve seen arson, sabotage and more,” he added.

On Iran, he said there had been an “unprecedented pace and scale” of plots over the past two years.

As events unfold in the Middle East, MI5 was giving its “fullest attention” to the risk of a rise in Iranian-state backed aggression in the UK, he added.

Overall, MI5 and the police have disrupted 43 late-stage attack plots since March 2017, saving “numerous lives”, he said, adding: “Some of those plotters were trying to get hold of firearms and explosives, in the final days of planning mass murder.”

In a wide-ranging speech, McCallum also blamed extreme right-wing ideologies for a “staggering” rise in the number of children being investigated for terrorism.

Under-18s represent 13 percent of people being investigated by the spy agency for possible involvement in terror activities, he said.

He told reporters at MI5’s Counter Terrorism Operations Centre in London that the number marked “a threefold increase in the last three years”.

McCallum said the internet was the “biggest factor” driving the rise, describing how easily youngsters can access “inspirational and instructional material” from their bedrooms.

He said the intelligence service was seeing “far too many cases where very young people are being drawn into poisonous online extremism”, singling out “canny” internet memes.

“Extreme right-wing terrorism in particular skews heavily towards young people, driven by propaganda that shows a canny understanding of online culture,” he added.

“It’s not really a consistent single ideology on the extreme right-wing side and that is what has skewed the numbers most heavily.”

The UK terrorist threat level remains at “substantial” — the third highest out of five — meaning an attack is likely.

McCallum added that the Islamic State group had “resumed efforts to export terrorism” and that in the last year inquiries into plots by hostile states had surged by 48 percent.