Yes, the UK faces threats from Russia and China but its future hinges on tackling a “crisis” which endangers the British spirit and Nigel Farage is the man for the job. That is the view of Reform UK’s new chief adviser on global affairs – the co-founder of a think tank dedicated to fighting extremism, advancing democracy and protecting “real human rights”.

The defection of Alan Mendoza from the Conservatives to Mr Farage’s party is among the latest signs that a growing number of serious-minded figures believe the veteran Brexiteer has a real chance of becoming Prime Minister. If Mr Farage does move into Number 10 he will face the challenge of protecting Britain at a time of global change and danger. Mr Mendoza sees Reform as a welcome source of badly needed “dynamism”.

“It’s coming from a new party that has a vision to transform and turn Britain around and to avert this terrible crisis that we are in,” he says. “That is the interesting bit of this, not that the Conservatives may have lost their way.”

He sees a direct link between the difficulty the Ministry of Defences faces recruiting members of the armed forces and Britain’s present “funk”.

People will not feel pride in the UK or be inspired to defend these borders, he warns, if they are “constantly told that the country is in a funk, that things are getting worse rather than better, or that we have to apologise for the sins of the past, that we have somehow done wrong to the world”.

It is vital Britain has the strength to deploy forces overseas, he argues, because “it might be that the strategic threat you face is somewhere away from your home shore and dealing with it there is a more appropriate and ultimately safer measure than waiting for it to come to you”.

Mr Mendoza wants Britons to know they live in “one of the greatest countries in the world” and it has a “glorious history”. He longs for the narrative of “decline and demise” to be challenged so the nation can look forward to a better future.

Mr Farage, he says, is “right in the mainstream of public opinion” and, after decades of political experiences, is the “finished article”.

“I think those talents he has are uniquely suited to this time when we have to turn around a crisis in short order,” he says. “And we need someone who understands what Britain is, and crucially, of course, what Britain can still be.”

He sprung to the Reform leader’s defence in the wake of allegations Mr Farage made anti-Jewish remarks as a schoolboy at Dulwich College.

He says he has never seen “any suggestion of that ever from him,” adding: “I’ve seen the contrary – I’ve seen him getting physically angry at the idea that antisemitism is on the rise and that Jews might have to leave the UK.”

Mr Mendoza, who is a councillor in the City of Westminster, says that when knocking doors he picks up on a sense of decline – in services, in civility and “public spirit”.

“That is actually alien to the British tradition,” he says. “We have always been an optimistic people. We have always quietly got on with things, secure in the knowledge the fundamentals are right, and that even in temporary times of trouble better times are ahead.”

This “sapping” of spirit is a source of concern when Britain faces a host of security threats. He sees China as the “far threat”, arguing the rising superpower has a desire to “control us” and the scale of espionage shows it is not a “friend” and “means us ill”.

The “near threat” is Russia. He claims the “big question” is whether Vladimir Putin – whom he says “doubled-down on a terrible mistake” – wants to spend the “rest of his life bogged down in a war in Ukraine”.

“It is down to vanity and down to a desire to cover up his own strategic miscalculation that he’s continued this war at terrible cost to both Ukraine and Russia,” he says.

He fears Putin is attempting to string along the West, using talks as a way to stop the seizure of Russian assets.

“This is a war that Russia started,” he says. “Russia could end it at any minute.”

While it is essential to arm Ukraine to keep the country “in the game”, he argues, sanctions and seizures which threaten to harm Russia’s economy are required to shift Putin’s position.

“You are always going to end up with some kind of agreed peace settlement,” he says. “The only question is when do the Russians come to it? Do they come to it voluntarily or do they come to it kicking and screaming?”

His day job at the Henry Jackson Institute involves thinking hard about threats to British lives and prosperity. Worries include attacks on underseas cables which are vital for Britain’s communications, drone assaults launched from within the UK and the country’s vulnerability to sabotage.

“It’s quite easy at fairly low cost to engage in sabotage within the UK,” he remarks.

Stressing that his new role with Reform will not damage the independence of the think tank, he says: “There are all shades of political opinions within our board of trustees and within our staff and we do what is right for Britain, not what is right for a political party.”

His political beliefs were shaped as a student at Cambridge, where his MPhil and PhD were supervised by Brendan Simms, the author of Unfinest Hour: Britain and the destruction of Bosnia. The book castigates the UK for standing aside and trying to defuse pressure for action in the face of ethnic cleansing; it argues this “terrible failure” must not be repeated.

Paying tribute to his professor, he says: “He had a major effect on my thinking because we shared that view.”

Mr Mendoza now has the chance to influence the strategy and policies of a party which has a towering lead in the polls. His ambition for Reform is nothing less than national revival.

“If they can rekindle the vigour and the energy of the British people, that is where we will have a victory that will last the ages,” he says. “That is what determines Britain’s success or failure – its people, their talents, and their belief in the country’s future.”