The West was too slow to act over Russian aggression in Ukraine, Boris Johnson has told Ukrainian MPs, according to the BBC.
Addressing the Ukrainian parliament via video link, he said Ukraine’s allies “cannot make the same mistake” as they did over the 2014 Crimea invasion.
He said the West had been “too slow to grasp what was really happening” and “failed” to collectively impose sanctions against Vladimir Putin.
Details of £300m of extra military aid were also announced by Mr Johnson.
The military aid to be sent to Ukraine in the coming weeks will include electronic warfare equipment, a counter-battery radar system, GPS jammers and night-vision devices.
Introduced to MPs in Kyiv by the Ukrainian parliament’s speaker, Mr Johnson said Ukraine’s allies must be “humble” as the nation was previously invaded in 2014 when Russia seized Crimea and began the war in Donbas.
“We cannot make the same mistake again,” he said.
The UK prime minister – the first international leader to address the parliament since the Russian invasion – praised Ukraine’s resistance for standing up to Russian forces.
He said: “You have exploded the myth of Putin’s invincibility and you have written one of the most glorious chapters in military history and in the life of your country.
“The so-called irresistible force of Putin’s war machine has broken on the immoveable object of Ukrainian patriotism and love of country.”
He also echoed the words of Prime Minister Winston Churchill, just as Ukraine’s President Volodymyr Zelenskyy did when he addressed MPs at Westminster in March.
Speaking to Ukrainian MPs in the chamber holding Ukrainian and Union flags, he said: “This is Ukraine’s finest hour, that will be remembered and recounted for generations to come.
“Your children and grandchildren will say that Ukrainians taught the world that the brute force of an aggressor counts for nothing against the moral force of a people determined to be free.”
Following the speech – which was delivered through an interpreter – the MPs in the Chamber stood to applaud and then President Zelensky described the UK and Ukraine as now being like “brothers”.
“It is not scary when such an evil enemy is against you if such a good friend is next to you. Such as Great Britain” the Ukrainian president said.
He also thanked more than a dozen British celebrities who had voiced their support for Ukraine – including Sir Elton John, Ed Sheeran and the Beckham family.
In an earlier interview with ITV’s Good Morning Britain, Mr Johnson said the UK was leading the world in helping Ukraine to “protect themselves”.
He said: “What the UK is doing – and has done since the crisis began – is lead the world in helping the Ukrainians protect themselves against barbaric aggression by Vladimir Putin. That’s all we’re doing.
“We’re not saying we’re doing this in order to drive some geopolitical change or to have an outcome in Moscow…
“What we care about is Ukrainian people and their suffering.”
When asked about the Ukrainian UK ambassador’s call for MPs to drop visa rules for refugees fleeing the country, the prime minister insisted it was important to “protect the system from those who might want to abuse it”.
A total of 86,000 visas have been issued, but only 27,000 refugees have arrived, Mr Johnson said. He said the UK could have reacted faster.