Boris Johnson has condemned Donald Trump’s “lies” about Ukraine – but still backed him to end the country’s war with Russia.

The former prime minister also said that claims Ukraine could have done a deal to end the conflict soon after Moscow’s 2022 invasion was a “great, big fat, steaming lie”.

Trump provoked international fury earlier this month by describing Ukrainian president Volodymyr Zelenskyy as a “dictator” and has even suggested that Kyiv was responsible for the war.

But appearing on Piers Morgan Uncensored, Johnson said: “Saying that Ukraine was responsible started this war, saying that Zelenskyy is a dictator, saying the Ukrainians could have done some deal early on in this war, got the Russians out, that wouldn’t have involved a complete humiliation for for Ukrainians, it’s just lies.

“It’s just rubbish, and it’s very painful for people who care about Ukraine, who actually know the facts, to listen to this stuff. But … I remain optimistic, nonetheless, that there is method in Donald Trump’s madness, and actually that by shaking things up in the way that he is, he can continue to drive the process of peace in Ukraine.”

Dismissing claims that he had dissuaded Ukraine from accepting a peace deal earlier in the war, Johnson said: “To say that I had some role in persuading the Ukrainians to fight for their country, is a great it’s obviously totally implausible, but it’s also great, big fat, steaming lie.”

Johnson also insisted that the war was “basically unwinnable” for Russia.

“After three years of war, Vladimir Putin has not, and will not, conquer this country,” he said. “In the last year all these lies that Putin is making inexorable process to progress towards victory. It is a great, big fat, steaming, stinking lie, Piers.

“In the last year, I think, he’s taken 0.5% of Ukrainian territory at a cost of about 420,000 troops. It is not going his way. He is not going to win. What we need is for Europeans to dial down some of their anxiety, some of the rhetoric.

“Everybody [needs] to dial down the rhetoric. Look at what Trump is actually proposing and do a deal that will guarantee Ukraine’s security for the long term, and reflect the reality which is for, I think for Putin this war is basically unwinnable.”