He's warned the UK faces the most 'complex' threat it has ever seen.

Ken McCallum took to the public in a rare appearance where he gave a speech raising awareness on the most "complex and interconnected" threat the UK had ever seen.

McCallum said that Russia's intelligence agency want to generate "sustained mayhem on British and European streets".

The director general went on to detail that the MI5 has responded to 20 Iran-backed plots since 2022 and said that the mix of terror-related threats and threats from whole nations have left MI5 with "one hell of a job on its hands".

He also gave the terrifying statistic that the intelligence agency has foiled 43 late-stage plots to commit "mass murder" in the UK since 2017, involving firearms and explosives.

McCallum said most of the work involved Islamic extremism while extreme right-wing terrorism followed behind.

He said counter-terrorism work remained split between "75% Islamist extremism, 25% extreme right-wing terrorism".

However, he added that there was a "dizzying range of beliefs and ideologies" dealt with by his agency.

He said: "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."

Meanwhile McCallum said that the number of state-threat investigations by MI5 had increased by 48% and accused Russia of "arson, sabotage and more dangerous actions" in the UK.

The director also disclosed that, following Russia's invasion of Ukraine, 750 Russian diplomats have been sent home packing with "a great majority of them" being spies.

The decision to expel so many diplomats has greatly hindered the Russia intelligence services' capability and professionalism with Russia turning to proxies such as private intelligence operatives to do "their dirty work".

McCallum was equally concerned by the amount of younger people taking part into online extremism with 13% of those involved being under the age of 18.

He said other issues MI5 encountered included the internet with much of the threat coming from “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.

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