UK Prime Minister Boris Johnson has written today that despite Vladimir Putin’s claims of Nato expansion, “the truth is that Ukraine had no serious prospect of Nato membership in the near future”.

Writing in the New York Times, Johnson dismissed Putin’s justification for his invasion of Ukraine as a “confected pretext” and said: “This is not a Nato conflict and it will not become one. No ally has sent combat troops to Ukraine.

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“We have no hostility towards the Russian people and we have no desire to impugn a great nation, a world power and a founding member of the United Nations. We despair of the decision to send young innocent Russians into a bloody and futile war.”

The PM said: “We were ready to respond to Russia’s stated security concerns through negotiation. I and many other Western leaders have spoken to President Putin to understand his perspective.”

He added: “It was now clear diplomacy never had a chance. But it is precisely because of our respect for Russia that we find the actions of the Putin regime so unconscionable.”

He warned: “We need to prepare now for even darker days ahead.”

Johnson also urged he had never “seen an international crisis where the dividing line between right and wrong has been so stark”.

In the New York Times, he urged world leaders to back his six point plan to tackle Putin.

“Have we done enough for Ukraine? The honest answer is no.”

“We must not allow anyone in the Kremlin to get away with misrepresenting our intentions to find post-facto justification for their war of choice,” Mr Johnson wrote.

“We have failed to learn the lessons of Russian behaviour that have led to this point. No one can say we were not warned: we saw what Russia did in Georgia in 2008, Ukraine in 2014 and even on the streets of the British city of Salisbury. And I know from speaking to my counterparts on recent visits to Poland and Estonia just how acutely they feel the threat.

“It is no longer enough to express warm platitudes about the rules-based international order. We are going to have to actively defend it against a sustained attempt to rewrite the rules by force and other tools such as economic coercion.”