Laurie Bristow returned to the UK from his post as amdassador to Afghanistan on one of the final flights out of the country, which is now under the control of the Taliban.
He said on Saturday that the time had come to end an airlift which had evacuated almost 15,000 Afghan and British citizens over the past two weeks.
On Friday, Britain had said its evacuation mission would end within hours and that its military would be unable to fly out any Afghan citizens eligible for resettlement who had not already entered Kabul airport.
Chief of Joint Operations, Vice Admiral Sir Benjamin John Key, said on the tarmac at Brize Norton that the end of evacuations was not a "moment of celebration".
"Of course the United States are still engaged in their own withdrawal and I would be very nervous at saying that we have completed a successful withdrawal from Afghanistan until all our allies and partners have returned. The United States has provided the framework for security in Kabul as part of a huge, international effort."
Britain's defence minister, Ben Wallace, predicted last week that time had run out to evacuate around 1,000 Afghans who were eligible to come to Britain, including former staff to the UK.
More than 450 British armed forces personnel died during two decades of deployment in the country.