The former prime minister told the BBC that US President Donald Trump’s policy of American “isolation” was creating a power vacuum that would embolden nations like Russia and China.

Sir John, who was PM from 1990 to 1997, said the gains made since the collapse of the Soviet Union were now being reversed – and that there was “no doubt” Russia would invade elsewhere before long.

He said that “ugly nationalism” growing concurrently was making for a “very unsettled time”.

His comments come as European leaders prepare for an emergency summit on Monday on the war in Ukraine.

US and Russian officials are due to open peace talks in the coming days despite concerns European nations including Ukraine were being locked out.

Sir John also rejected US Vice-President JD Vance’s recent criticism of Europe’s record on free speech, suggesting the remarks should have been directed at the authorities in Moscow or Beijing.

He told BBC Radio 4’s The World This Weekend: “It’s extremely odd to lecture Europe on the subject of free speech and democracy at the same time as they’re cuddling [Russian President Vladimir] Putin.

“In Mr Putin’s Russia, people who disagree with him disappear, or die, or flee the country, or – on a statistically unlikely level – fall out of high windows somewhere in Moscow.”

Sir John said the world was changing and “may not be reshaping in a way that is congenial to the West”.

He continued: “Many of the gains we made over recent years, when the Soviet Union collapsed, are now being reversed and you see a very aggressive Russia again in Ukraine.

“And if they were to succeed with their venture in Ukraine, no doubt they’d be elsewhere before too long.

“There is no doubt in my mind that democracy has been in modest decline over the last 18 years.

“There is an ugly nationalism growing, mostly from the intolerant right… So it is a very unsettled time.”

The former Conservative leader, who presided over a tumultuous time for the UK’s economy, said he sympathised with the challenges the current Chancellor Rachel Reeves faced, but said the global situation may require more defence funding.

“It’s very, very easy to say from outside government, ‘I’d just do this and I’d spend all this money’.

“I would prefer to say I would realise in my plans that we have to make a very material increase in the level of defence expenditure and do it as a priority as soon as it is credible to do so.”

Speaking earlier on the BBC’s Sunday with Laura Kuenssberg programme, Business Secretary Jonathan Reynolds said the UK and Europe had to respond to US demands for them to pay more towards their “collective defence” in the face of “greater threats”.

He said the government would set out a roadmap to increase defence spending from 2.3% to 2.5% of the nation’s economic output, but declined to offer a definitive timetable.

Reynolds also played down divisions between the US and its allies over resolving the Ukraine conflict, insisting there was “still a great deal of common ground”.

Sir John has made public interventions on a number of issues in recent years, including Russia’s full-scale invasion of Ukraine, which started in 2022.

Shortly after the war began, he and another former prime minister, Gordon Brown, were among signatories of a petition calling for Putin to face a Nuremberg-style trial for war crimes over his actions in Ukraine.