Russian military intelligence is seeking to cause “mayhem” across Britain and Europe, the UK’s domestic spy chief said on Tuesday, while a growing threat from al-Qaeda and Islamic State was his greatest terrorism concern.

In an annual speech, Security Service (MI5) Director General Ken McCallum also accused Iran of being behind “plot after plot” on British soil.

McCallum said state threat investigations were up 48 per cent in the last year as Russia and Iran turned to criminals, drug traffickers and proxies to carry out their “dirty work”.

“It will be clear to you that MI5 has one hell of a job on its hands,” he said.

Outlining the threats to Britain, McCallum said since March 2017, MI5 and the British police had disrupted 43 late-stage plots, some of which were in the final days of planning for mass murder.

The terrorist trend which the spy chief said concerned him most was a worsening threat from al-Qaeda, seeking to capitalise on the conflict in the Middle East, and especially Islamic State, which had resumed efforts to export terrorism, citing the attack on a Moscow concert hall in March.