So-called Islamic State terrorists struggled to promote their ideology of hate online after the UK launched its first "major offensive cyber-campaign" against the extremists, the head of GCHQ has revealed.

The covert operation, which is "too sensitive to talk about in detail", hindered the group's ability to co-ordinate attacks and suppressed their propaganda, former MI5 senior officer Jeremy Fleming said.

Mr Fleming, speaking for the first time since becoming head of GCHQ last year, 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."

Mr Fleming told attendees at CYBERUK18, a conference hosted by the National Cyber Security Centre (NCSC), that UK intelligence efforts had disrupted the group's online activities and even destroyed 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," he said.

Mr Fleming also gave an overview of the changing threats amid the unrelenting pace of technological advances, which challenges UK national security.

Pointing the finger at Russia, he said the Salisbury poisonings showed how "reckless" the Kremlin was prepared to be and accused Vladimir Putin of not "playing by the same rules".

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.