Boris Johnson has argued that continued international support for Ukraine is a price worth paying, saying that to let Russia prevail would be “absolutely chilling” for nearby countries and usher in a period of global anxiety.

Likening the need to oppose Russia to the situation in the second world war, Johnson said that while opposing fascism brought enormous costs, it then created decades of prosperity and stability.

The need for long-term support for Ukraine is one of Johnson’s key messages at the G7 summit of world leaders in Bavaria, Germany. The issue was set to be discussed on Monday with Volodymyr Zelenskiy, the Ukraine president, due to address the gathering virtually.

Speaking to BBC News, Johnson said there was a need for “strategic endurance”, predicting that even if the war continued, “the economic impacts on the UK will start to abate”.

He said: “But just in terms of staying the course, imagine if we didn’t. Imagine if we allowed Putin to get away with the violent acquisition of huge chunks of another country, a sovereign independent territory – the lessons for that would be absolutely chilling in all of the countries of the former Soviet Union.

“In terms of the economic effects, that would mean long-term instability, and anxiety across the world.”

Overall, the prime minister argued, “the price of freedom is worth paying”. He said: “Just remember, it took the democracies in the middle of the last century a long time to recognise that they had to resist tyranny and aggression. It was very expensive.

“But what it bought in the end, with the defeat of the dictators, particularly of Nazi Germany, it bought decades and decades of stability, a world order that relied on a rules-based international system. And that is worth protecting, that is worth defending, and that delivers long-term prosperity.”

Johnson has said G7 leaders are united on the issue, although it remains to be seen if the summit, which ends on Tuesday, will deliver any notable concrete achievements in areas such as new sanctions, or efforts to get millions of tonnes of Ukrainian grain out of a Russian blockade.

At the gathering, Johnson has warned against a temptation to push Zelenskiy into potentially accepting a deal that would bring peace in exchange for Russian control of eastern areas in Ukraine, saying no other countries could make such a choice.

“You can’t be more Ukrainian than the Ukrainians,” he told the BBC. “And I think it is for Volodymyr Zelenskiy and his people to decide what they want. And what they want is their land, they want their country to be able to live in peace and freedom.

“And I totally support that. And so I think the difficulty is that no one here at the G7 can really see any alternative to simply supporting them in regaining their sovereignty.”