Russia's intelligence agency has been on a mission to generate "sustained mayhem on British and European streets", the head of MI5 has said.

Giving his annual update on security threats faced by the UK, Ken McCallum said GRU agents had carried out "arson, sabotage and more dangerous actions conducted with increasing recklessness" in Britain after the UK backed Ukraine in its war with Russia.

MI5 had also responded to 20 plots backed by Iran since 2022, he said, although he added the majority of its work still mostly involved Islamist extremism followed by extreme right-wing terrorism.

The complex mix of terror-related threats and threats from nation states meant MI5 had "one hell of a job on its hands", he warned.

In a wide-ranging speech, he said:

? Young people were increasingly being drawn into online extremism, with 13% of those investigated for terrorism involvement aged under 18

? A total of 43 late-stage plots involving firearms and explosives to commit "mass murder" in the UK had been foiled since 2017

? The number of state-threat investigations by MI5 had increased by 48%

? Counter-terrorism work remained split between "75% Islamist extremism, 25% extreme right-wing terrorism"

There was a "dizzying range of beliefs and ideologies" MI5 had to deal with, he told the briefing at MI5's counter-terrorism operations centre in London.

"The first 20 years of my career here were crammed full of terrorist threats.

"We now face those alongside state-backed assassination and sabotage plots, against the backdrop of a major European land war," he said.

The UK's "leading role" in supporting Ukraine means "we loom large in the fevered imagination of Putin's regime" and further acts of aggression on UK soil should be expected, he warned.

The UK's current terror threat level is substantial - meaning an attack is likely.

How do terrorism threat levels work?

More than 750 Russian diplomats had been expelled from Europe since Russia?s invasion of Ukraine, "the great majority of them" spies, Mr McCallum said.

This affected the Russian intelligence services' capability, he explained, and added that diplomatic visas had been denied to those who Britain and allies considered Russian spies.

Russian state actors turned to proxies, such as private intelligence operatives and criminals, to do "their dirty work", but this affected the professionalism of their operations and made them easier to disrupt.

While Mr McCallum has spoken publicly before about both the Russian and Iranian threats, he has not previously accused Moscow in such stark terms.

On Iran, he said the 20 Iran-backed plots MI5 had responded to presented "potentially lethal threats to British citizens and UK residents".

He said that since the 2022 killing of Mahsa Amini - the 22-year-old who died in Iranian police custody after being arrested for allegedly violating rules requiring women to wear the headscarf - "we?ve seen plot after plot here in the UK, at an unprecedented pace and scale".

In a previous public address he referred to 10 plots against Iranians in the UK.

That number has now doubled, implying that Iranian state activity is undeterred by the threat of being caught.

He added that, as the war in the Middle East continues, MI5 would give its "fullest attention to the risk of an increase in ? or a broadening of ? Iranian state aggression in the UK".

In both cases, Russia and Iran, the MI5 boss stressed that because it was difficult - to almost impossible - for their accredited diplomats to carry out such actions, they were turning increasingly to underworld criminal gangs.

Speaking about China, he said the economic relationship with the UK helped to underpin security.

However, he later told reporters the Chinese Communist Party (CCP) had a programme to steal data and information, and "we have seen 20,000 obfuscated approaches to individuals by China".

'Canny understanding of online culture'

The number of young people being drawn into online extremism is growing, Mr McCallum warned.

About 13% of those investigated for involvement in terrorism were under 18 - a threefold increase in the last three years.

The security agency was seeing "far too many cases where very young people are being drawn into poisonous online extremism".

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

Responding to questions from reporters, he reiterated concerns about the role of the internet being the "biggest factor" driving the trend, and described how easily youngsters could access material from their bedrooms.

A high proportion of the threat was made up by ?lone individuals indoctrinated online" he said.

?In dark corners of the internet, talk is cheap. Sorting the real plotters from armchair extremists is an exacting task,? he said.

?Anonymous online connections are often inconsequential, but a minority lead to deadly, real world actions.?

Home Office figures published last month show that of 242 people detained on suspicion of terror offences in the year to June, 17% (40) were aged 17 and under.

Sir Keir Starmer acknowledged the "sober findings" outlined by Mr McCallum but said the public should be "reassured that our security services are world class and will do everything necessary to keep us safe." (BBC)

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