Islamic State terrorists struggled to promote their ideology of hate online after the UK launched its first cyber campaign against the extremists, the head of the UK intelligence service has said.

Ex-MI5 senior officer Jeremy Fleming, in his first public speech since becoming head of GCHQ last year, said the UK cyber attack on IS, also known as Daesh, was “too sensitive to talk about in detail” but his organisation and the Ministry of Defence had conducted a “major offensive”.

Mr Fleming, speaking in Manchester, said: “These operations have made a significant contribution to coalition efforts to suppress Daesh propaganda, hindered their ability to coordinate attacks, and protected coalition forces on the battlefield.

“Cyber is only one part of the wider international response.

“But this is the first time the UK has systematically and persistently degraded an adversary’s online efforts as part of a wider military campaign.

“Did it work? I think it did.”

He said: “The outcomes of these operations are wide ranging.

“We may look to deny service, disrupt a specific online activity, deter an individual or a group, or perhaps destroy equipment and networks.

“In 2017 there were times when Daesh found it almost impossible to spread their hate online, to use their normal channels to spread their rhetoric, or trust their publications.

“Of course, the job is never done – they will continue to evade and re-invent.

“But this campaign shows how targeted and effective offensive cyber can be.”

Mr Fleming, speaking at CYBERUK18, a conference hosted by the National Cyber Security Centre (NCSC) gave an overview of the changing threats amid the unrelenting pace of technological advances, which challenges UK national security.

He added: “Hostile states, terrorists and criminals are emboldened and assisted by technology.”

He said the Salisbury poisonings showed how “reckless” Russia was prepared to be, accusing the Kremlin of not “playing by the same rules”.

Mr Fleming said cyber has become an indispensable part of modern national security statecraft and the UK had to continue to work with the EU and Nato to face the challenge.

He concluded: “The challenges we face are vast. I’ve set out the significant changes in the threats the UK faces and which GCHQ exists to combat.

“And the ever faster and more diverse rate of technological change that we must understand if we are to be successful.”

But he said the UK could draw on a breadth of “excellence and expertise” within the intelligence services, military and police, both in the UK and with allies to help keep the nation safe.

He added: “We’re building a strong and confident GCHQ. It’s transparent and open when it can be.

“It always acts lawfully.

“And it’s using cutting-edge technology and technologists to meet the challenges the second century of our service to this country will bring.”