ISIS and al Qaeda present a “resurgent” threat to the United Kingdom, the head of the country’s domestic security service warned in a rare public intervention on Tuesday, as he outlined a changing landscape of terrorism that is increasingly relying on children and on the internet.

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.

The head of Britain's domestic spy agency accused Russian military intelligence of being on a "sustained mission to generate mayhem."