And Alex Younger says Russia's actions in Syria is creating a breeding ground for terrorists.

In a wide-ranging and rare speech at MI6's new headquarters in central London, Mr Younger, or "C" as he is referred to, said the internet had opened up a new frontier he called "the increasingly dangerous phenomenon of hybrid warfare."

"The connectivity that is at the heart of globalisation can be exploited by states with hostile intent to further their aims deniably," Mr Younger said.

"They do this through means as varied as cyber-attacks, propaganda or subversion of democratic process."

US intelligence officials have accused Russia of orchestrating the hackings of emails related to the Democratic Party during the presidential campaign, to destabilise the US's democratic processes. The emails were leaked through various websites, including WikiLeaks.

"The risks at stake are profound and represent a fundamental threat to our sovereignty; they should be a concern to all those who share democratic values," Mr Younger said.

Russia has also been accused of orchestrating damaging fake news campaigns online, through websites and armies of online "trolls" who flood social media sites like Reddit, Facebook and Twitter with false information. The Kremlin denies interfering the US elections.

Mr Younger did not name a particular state when he spoke of the "hybird warfare phenomenon" but did single out Russia for its actions in Syria and said the military campaign being waged by Bashar al-Assad and Vladimir Putin is creating a new breed of terrorists.

"I believe the Russian conduct in Syria, allied with that of Assad's discredited regime, will, if they do not change course, provide a tragic example of the perils of forfeiting legitimacy," he said.

"In defining as a terrorist anyone who opposes a brutal government, they alienate precisely that group that has to be on side if the extremists are to be defeated."

"Meanwhile, in Aleppo, Russia and the Syrian regime seek to make a desert and call it peace. The human tragedy is heartbreaking".

"We should, all of us, including intelligence officers, approach analysis of Syria with humility. The facts on the ground are staggeringly complex. "

"The plight of Syrians continues to worsen.  I cannot say with any certainty what the next year will bring.  But what I do know is this: we cannot be safe from the threats that emanate from that land unless the civil war is brought to an end."

'Scale of the threat is unprecedented'

Mr Younger said counter-terorrism was a "niche activity" when he joined the service in 1991. "It is now one of MI6's three headline missions," he said.

He said 12 terrorists plots in the UK had been foiled since June 2013.

"As I speak, the highly organised external attack planning structures within Daesh, even as they face military threat, are plotting ways to project violence against the UK and our allies without ever having to leave Syria," he said.

'Conflicted about Bond'

He also revealed that as the real life "C" he is "conflicted about Bond," the fictional hit film series featuring the risk-taking and promiscuous spy James Bond.

"There are a few aspects of the genre that do resonate in real life; fierce dedication to the defence of Britain, for example. The real-life 'Q' would want me to say that we too enjoy (and indeed need) a deep grasp of gadgetry."

"But that's pretty much where the similarity ends. And, were Mr Bond to apply to join MI6 now, he would have to change his ways."

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