Boris Johnson is facing calls for a last-ditch intervention to prevent the complete collapse of Afghanistan as Taliban fighters were reported to have entered the outskirts of Kabul.
The lead elements of the British force sent to evacuate the remaining UK nationals were understood to be in the capital amid fears it could fall within days or even hours.
In a sign of the speed of the collapse, arrangements were reportedly being made to fly the British ambassador Sir Laurie Bristow out of the country.
It had previously been intended that he should remain in a secure location at Kabul airport along with other international diplomats.
But amid a hurried scramble for safety, helicopters were seen landing at the US embassy to ferry away remaining personnel.
In the UK, there was deep anger among many MPs at the way – 20 years after the first international forces entered Afghanistan – the country was being abandoned to its fate.
The chairman of the Commons Foreign Affairs Committee Tom Tugendhat said it was “the biggest single foreign policy disaster” since Suez, while Defence Committee chairman Tobias Ellwood said it was a humiliation for the West.
Despite the decision of the Biden administration to withdraw the remaining US troops which triggered the collapse, Mr Ellwood said it was still not too late to turn the situation around.
He called for the despatch of the Royal Navy carrier strike group to the region and urged the Prime Minister to convene an emergency conference of “like-minded nations” to see what could be done.
“I plead with the Prime Minister to think again. We have an ever-shrinking window of opportunity to recognise where this country is going as a failed state,” he told Times Radio.
“We can turn this around but it requires political will and courage. This is our moment to step forward.
“We could prevent this, otherwise history will judge us very, very harshly in not stepping in when we could do and allowing the state to fail.”
Labour leader Sir Keir Starmer said the situation in Afghanistan was “deeply shocking” and called on the Government to recall Parliament.
“We need Parliament recalled so the Government can update MPs on how it plans to work with allies to avoid a humanitarian crisis and a return to the days of Afghanistan being a base for extremists whose purpose will be to threaten our interests, values and national security,” he said.
Earlier Defence Secretary Ben Wallace said that when the US announced its plans to withdraw, he had approached other allies about taking their place but none was willing to do so.
Writing in The Sunday Telegraph, he said it was “arrogant” to think the UK – which is also pulling out its troops – could resolve the situation unilaterally.
“A unilateral force would very quickly be viewed as an occupying force and, no matter how powerful the country that sends it, history shows us what happens to them in Afghanistan,” he said.
Britain is sending 600 troops – including Paras from 16 Air Assault Brigade – on a mission to support the final departure of the remaining UK nationals as well as Afghans who worked with the UK in the country.
Mr Tugendhat, who served as an Army officer in Afghanistan, said the priority had to be to get as many people out before Kabul collapsed.
“This isn’t just about interpreters or guards. This is about those people who we trained in special forces to serve alongside us, those who helped us to understand the territory through our agencies and our diplomats,” he told BBC News.
“This is the people who, on our encouragement, set up schools for girls. These people are all at risk now.
“The real danger is that we are going to see every female MP murdered, we are going to see ministers strung up on street lamps.”