Britain and its allies have uncovered a “staggeringly reckless” Russian sabotage campaign against Europe, the head of MI6 has said.

Sir Richard Moore, known as “C”, used a speech on Friday to accuse Russia of behaving in a way that was “dangerous and beyond irresponsible”.

He said: “We have recently uncovered a staggeringly reckless campaign of Russian sabotage in Europe, even as Putin and his acolytes resort to nuclear sabre-rattling to sow fear about the consequences of aiding Ukraine and challenge western resolve.”

Affirming that Ukraine had “the will to win”, Sir Richard said British and French intelligence had been “critical” in helping their leaders “navigate successfully (Vladimir) Putin’s mix of bluster and aggression”.

In the context of concern that a Donald Trump presidency in the US could see support for Ukraine decline, he added: “The cost of supporting Ukraine is well known, but the cost of not doing so would be infinitely higher.

“If Putin succeeds, China would weigh the implications, North Korea would be emboldened and Iran would become yet more dangerous.”

He made his comments during an event at the British embassy in Paris, where he appeared alongside French intelligence chief Nicolas Lerner to celebrate 120 years of the Entente Cordiale between Britain and France.

Sir Richard hailed the strength of that relationship as he said the threats facing Europe “could hardly be more serious”.

He said: “In 37 years in the intelligence profession, I have never seen the world in a more dangerous state.”

As well as the threat from Russia, Sir Richard warned that the West still faced a “full reckoning” with the “radicalising impact” of the renewed outbreak of hostilities in the Middle East following Hamas’s attack on Israel in October 2023, while so-called Islamic State was “expanding its reach” after defeat in Syria and Iraq.