The last remaining United Kingdom troops began landing back from Kabul in Britain on Sunday, ending the country's 20-year military campaign in Afghanistan where the Taliban have seized power.
The Taliban insurgents stormed across the country on August 15, capturing all major cities in a matter of days, two weeks before the United States was set to complete its troop withdrawal after a costly two-decade war.
A Royal Air Force plane left Kabul airport on Saturday night and arrived at RAF Brize Norton in Oxfordshire, including with British ambassador to Afghanistan Sir Laurie Bristow who had been assisting the evacuation process.
Vice-Admiral Sir Ben Key, who ran the UK's evacuation dubbed Operation Pitting, said there was a "sense of sadness that we haven't done all we would have wished".
In a video posted on Twitter on Sunday morning, Prime Minister Boris Johnson said the end of Operation Pitting was the "culmination of a mission unlike anything we've seen in our lifetimes", and that British troops and officials had "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,” said Johnson. "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," he said.
In a letter to the armed forces community, Johnson acknowledged the fall of Kabul to the Taliban would have been hard for them to watch and "an especially difficult time for the friends and loved ones of the 457 service personnel who laid down their lives" during the war.
He noted that the UK's involvement in Afghanistan "kept Al Qaeda from our door for two decades and we are all safer as a result".
Paying tribute to the efforts of UK forces since 2001, he added: "Though we would not have wished to leave in this way, we have to recognise that we came in with the United States, in defence and support of the US and the US military did the overwhelming bulk of the fighting.”
"Together with our allies in America and Europe and around the world, we will engage with the Taliban not on the basis of what they say but what they do,” Johnson said.
Describing the conclusion of the military campaign launched by former British prime minister Tony Blair as a time for reflection, Johnson reiterated a previous statement that if the new regime in Kabul wanted diplomatic recognition, or to unlock the billions that are currently frozen, they will have to ensure “safe passage” for those who wish to leave the country, to respect the rights of women and girls and to prevent Afghanistan from becoming “an incubator for global terror”.
Writing in ‘The Sunday Telegraph', Foreign Secretary Dominic Raab said the UK was ready to consider sanctions against the militants -- but this would "depend on the choices the Taliban make on key issues" -- including on enabling safe passage out of the country.
The UK government has said it intends to re-establish a diplomatic presence in Kabul "as soon as the security and political situation in the country allows".
Downing Street said the number of people evacuated from Afghanistan included about 2,200 children, with the youngest born to an Afghan refugee on one of the evacuation flights.
About 5,000 British nationals and their families were airlifted, alongside more than 8,000 Afghan former UK staff and their families and those considered at risk from the Taliban.
It has been the UK's largest military evacuation since World War II.
UK Defence Secretary Ben Wallace has said he thought between 800 and 1,100 eligible Afghans would be left behind, along with around 100 to 150 Britons – although he said some of those were staying willingly.