Prime Minister Boris Johnson has said the UK departure from Afghanistan was “the culmination of a mission unlike anything we’ve seen in our lifetimes”.

The final UK troops and diplomatic staff were airlifted from Kabul on Saturday, drawing to a close Britain’s 20-year engagement in Afghanistan and a two-week operation to rescue UK nationals and Afghan allies.

Ambassador to Afghanistan Sir Laurie Bristow, who had been processing those fleeing the country at the airport until the last moment, was among those who landed at RAF Brize Norton base in Oxfordshire on Sunday morning.

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And it brought to a close Operation Pitting, believed to be the largest evacuation mission since the Second World War.

In a video uploaded to Twitter on Sunday morning, Mr Johnson praised the more than 1,000 military personnel, diplomats and officials who took part in the operation in Afghanistan.

He said: “UK troops and officials have worked around the clock to a remorseless deadline in harrowing conditions.

“They have expended all the patience and care and thought they possess to help people in fear for their lives.

“They’ve seen at first-hand barbaric terrorist attacks on the queues of people they were trying to comfort, as well as on our American friends.

“They didn’t flinch. They kept calm. They got on with the job.

“It’s thanks to their colossal exertions that this country has now processed, checked, vetted and airlifted more than 15,000 people to safety in less than two weeks.”

The Government said of the 15,000 people evacuated since the Taliban seized Kabul, 5,000 of those were British nationals and their families.

More than 8,000 Afghans who helped the British effort as interpreters or in other roles, or who are otherwise vulnerable to persecution by the regime, were also able to flee to safety with their families.

But Vice Admiral Ben Key, Chief of Joint Operations, who commands Operation Pitting, admitted there was a “sense of sadness” that not all could be saved.

Speaking at RAF Brize Norton on Sunday morning, he said: “Whilst we recognise and I pay testament to the achievement of everything that has been achieved by coalition forces, but particularly the British contingent, over the last two weeks, in the end we know that there are some really sad stories of people who have desperately tried to leave that we have – no matter how hard our efforts – we have been unsuccessful in evacuating.”

He added: “There has been a phenomenal effort achieved in the last two weeks. And I think we always knew that somewhere we would fall just short.

“So, this isn’t a moment of celebration for us at all, this is a moment to mark a tremendous international effort to evacuate as many people as we could in the time available.”

Addressing the families and loved ones of the British troops who “gave their all”, Mr Johnson said: “Your suffering and your hardship were not in vain.”

He added: “It was no accident that there’s been no terrorist attack launched against Britain or any other western country from Afghanistan in the last 20 years.

“It was thanks to the bravery of our Armed Forces who fought to knock out (Osama) Bin Laden’s networks.

“Thanks to the devotion of British troops and aid workers and diplomats and others, we’ve helped educate 3.6 million girls.

“Whatever the future may hold for Afghanistan, they will have that gift for the rest of their lives, a gift they will pass on to their daughters as well as their sons.”

But Conservative MP and veteran Tobias Ellwood said the UK had “very little to show” for 20 years in Afghanistan.

The chairman of the Commons Defence Select Committee told LBC: “Our armed forces performed so valiantly but they were let down by their political masters.

“We lacked the strategy, the statecraft, the patience to see through, and the manner of our departure is a humiliation, a confirmation of our diminished resolve, and our adversaries will not be slow to exploit it.”

He warned that “terrorism will raise its ugly face again” and “until we defeat this ideology, we can have as many drone strikes as we like, we can invade as many countries as we like, we will never win”.

Mr Ellwood added: “Unfortunately, we’ve made the situation worse, by absenting ourselves from the very place where it’s now very easy for terrorist groups to do their work.”