Isis and its ideology of violence “has absolutely not been defeated” and the threat of terrorism continues to proliferate with lethal effect, the head of Britain’s military has warned.

General Sir Nick Carter pointed to last week’s attack at London Bridge by freed Islamist terrorist Usman Khan as an example of the grave danger being faced by the public, and stressed that “conditions in parts of the world are not conductive to reducing the growth of extremism”.

In fact the security situation is getting worse, the chief of the Defence Staff held in his annual lecture at the Royal United Services Institute (RUSI) in London. He reminded the audience of his message last year that “instability was the defining condition with threats to our nation diversifying, proliferating and intensifying very rapidly”.

Speaking on Thursday evening, he continued: “So what’s changed? If anything, events over the past 12 months suggest the [situation] has become even less stable.”

Gen Carter’s caution against writing off Isis – a view echoed by other British, American and other western military commanders and politicians – is in marked contrast to Donald Trump’s declarations that “Isis has been 100 per cent defeated”.

London Bridge attack: Terror police shoot man after stabbing Show all 29 1 /29 London Bridge attack: Terror police shoot man after stabbing London Bridge attack: Terror police shoot man after stabbing Bystanders and police surrounding a person at the scene of an incident on London Bridge HLOBlog/PA London Bridge attack: Terror police shoot man after stabbing Police and emergency services PA London Bridge attack: Terror police shoot man after stabbing Armed police on London Bridge Twitter London Bridge attack: Terror police shoot man after stabbing A bystander holding a knife after police surrounded a person at the scene HLOBlog/PA London Bridge attack: Terror police shoot man after stabbing People fleeing from Borough Market PA London Bridge attack: Terror police shoot man after stabbing Police during the incident Twitter London Bridge attack: Terror police shoot man after stabbing A white truck across part of London Bridge SophK05/PA London Bridge attack: Terror police shoot man after stabbing A British Transport Police officer runs after reports of an incident Getty London Bridge attack: Terror police shoot man after stabbing Boats from the Metropolitan Police Marine Policing Unit patrol near the scene Getty Images London Bridge attack: Terror police shoot man after stabbing A lorry on the bridge crosses over lanes Luke Poulton via Reuters London Bridge attack: Terror police shoot man after stabbing Members of the police and emergency services arriving at Monument tube station AFP via Getty Images London Bridge attack: Terror police shoot man after stabbing Members of the public held behind a police cordon Getty Images London Bridge attack: Terror police shoot man after stabbing Police at the scene PA London Bridge attack: Terror police shoot man after stabbing Police evacuate people from Borough Market AP London Bridge attack: Terror police shoot man after stabbing Police surrond a part of the bridge Timothy Johnson/Twitter London Bridge attack: Terror police shoot man after stabbing A person is assisted after falling when Police evacuated people from Borough Market AP London Bridge attack: Terror police shoot man after stabbing A Police Officer cordons off London Bridge Station Getty Images London Bridge attack: Terror police shoot man after stabbing Members of staff are ushered into a Fitness First gym Getty Images London Bridge attack: Terror police shoot man after stabbing Handout photo taken with permission from the twitter feed of @ShashD of police at the scene of an incident on London Bridge in central London. PA Photo. Issue date: Friday November 29, 2019. See PA story POLICE LondonBridge. Photo credit should read: Shash/Twitter/PA Wire NOTE TO EDITORS: This handout photo may only be used in for editorial reporting purposes for the contemporaneous illustration of events, things or the people in the image or facts mentioned in the caption. Reuse of the picture may require further permission from the copyright holder. Shash/Twitter PA London Bridge attack: Terror police shoot man after stabbing People head away from the vicinity of Borough Market PA London Bridge attack: Terror police shoot man after stabbing Office workers look out of a window at a scene EPA London Bridge attack: Terror police shoot man after stabbing Armed police at the scene of an incident on London Bridge in central London. PA Photo. Picture date: Friday November 29, 2019. See PA story POLICE LondonBridge. Photo credit should read: Dominic Lipinski/PA Wire Dominic Lipinski PA London Bridge attack: Terror police shoot man after stabbing Men in forensics suits walk away from the site REUTERS London Bridge attack: Terror police shoot man after stabbing People are evacuated from London Bridge PA London Bridge attack: Terror police shoot man after stabbing ArrowontheHill ArrowontheHill/Twitter London Bridge attack: Terror police shoot man after stabbing Police at the scene of an incident on London Bridge PA London Bridge attack: Terror police shoot man after stabbing Armed police on the scene Alexandra Carr /SWNS.COM London Bridge attack: Terror police shoot man after stabbing Buses on London Bridge during the incident AFP via Getty Images London Bridge attack: Terror police shoot man after stabbing Police on the scene @joebxggs /SWNS.COM

The US president has used that argument to announce pulling US troops out of Syria – a move which resulted in Kurdish groups which had fought alongside American and western forces being left to face an onslaught by the Turkish military.

At this week’s Nato summit in the UK, Emmanuel Macron publicly challenged Mr Trump’s assertions on the issue. Speaking of the need to keep confronting Isis, the French president said the “number one priority, because it’s not yet finished, is to get rid of Isis and these terrorist groups ... It’s not yet done. I’m sorry to say that.”

Another cause of instability, said Gen Carter, was the aggressive behaviour of authoritarian regimes. “The multi-lateral system that has assured our security, stability and prosperity for several generations continues to be undermined by assertive authoritarian regimes who behave as if their historic right of entitlement is being denied them,” he stated.

There is a return to “great-power competition” and “the challenge for us in the west is that the character of that competition, being conducted by authoritarian opponents, is attacking our way of life and our freedom in a manner that is remarkably difficult to defeat without undermining the very freedoms we want to protect.

“There is a growing consensus that that the idea of ‘political warfare’ has returned. This is a strategy that is designed to undermine cohesion, erode economic, political and social resilience, and challenge our strategic position in key regions of the world.”

Russia’s activities in the North Atlantic, he pointed out, “is at a post-Cold War high”. Outside Europe there is continued turbulence, with Turkish incursions into Syria, attacks on oil tankers in the Persian Gulf, and wide-ranging protests in Iraq, Lebanon and other countries in the Middle East.

Socio-economic factors are creating conditions for extremism, said the general. “The IMF and the Brenthurst Foundation state that 62 per cent of the population of sub-Saharan Africa is under the age of 25; by 2030 the population will be around 1.65 million, and by 2050 it will have doubled from today to around 2.1 billion, with some 900 million living in cities.

“Poor governance, conflict, parlous economic growth and climate change suggest that population displacement and migration will increase significantly from the relatively small numbers we have seen so far. And of course, none of this is helped by great power competition and a new scramble for Africa’s resources.”

Both the major parties in the current election campaign, Gen Carter pointed out, have said they would carry out a strategic defence and security review in government.

The challenges and threats being faced, he stated, “requires a strategic response that integrates all of the levers of national power – a ‘fusion’ approach that brings coherence and consistency to our UK strategy.