The West was too slow to act over Russian aggression in Ukraine, Boris Johnson has told Ukrainian MPs.

Addressing the Ukrainian parliament via video link, Prime Minister Boris Johnson said Ukraine's allies "cannot make the same mistake" as they did over the 2014 Crimea invasion. Adding the West had been "too slow to grasp what was really happening" and "failed" to collectively impose sanctions against Vladimir Putin.

Mr Johnson is also announcing a new £300million package of military support as he underlines the UK's backing for Volodymyr Zelenskyand his brave fighters.

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 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."

The MPs gave the premier a succession of standing ovations, with one saying Ukraine was 'lucky to have a friend like the UK'.

In another symbolic move, the British ambassadorMelinda Simmons - who only recently returned to Kyiv - was present in person to hear the address.

Ms Simmons tweeted a photo of the scene saying it was 'ahuge privilege' to be at the session, although she later deleted it.

The appearance comes after Mr Johnson's surprise visit to the Ukrainian capital last month.