British military figures and policymakers expressed concern on Friday as Afghanistan's collapse to advancing Taliban fighters exposed the security failures of a decades-long intervention in the country.
Officials said Boris Johnson on Friday would host an emergency security meeting in the Cobra rooms in Whitehall for a discussion with top advisers on the risks emerging in Afghanistan. The Taliban were reported to be in control of 19 of the country's 34 provincial capitals, including Kandahar, Afghanistan's second biggest city. The lightning advance has come just weeks after US and Nato troops announced their full withdrawal from the region.
The UK's defence minister said he was worried that Afghanistan could become a breeding ground for terrorist groups such as Al Qaeda, but said there was no readily available military options to reverse the Taliban momentum.
The rapid advance of the extremist movement is being keenly felt in the UK, which played a key role in the Nato coalition launched in 2001. A former head of the UK armed forces, Gen David Richards, who commanded Nato troops in Afghanistan 15 years ago, told BBC's Newsnight he was “almost ashamed that we are in this position”.
"I'm absolutely worried that failed states are breeding grounds for those types of people," UK Defence Secretary Ben Wallace told Sky News when asked about Afghanistan, predicting that "al Qaeda will probably come back".
About 600 UK troops are stationed in the country to help British citizens and local translators get out of the country.
The British embassy in Kabul will be moved to a more secure location and will be run by core staff only.
Former international development secretary Rory Stewart described the collapse as "total betrayal" by the United States and the UK.
"I think the first thing to understand is that we stopped combat operations in 2016. People are pretending this is somehow Vietnam or Iraq," he told Sky News on Friday.
"This was not [a] 100,000 soldier operation. There have been very, very few casualties in the last five years. It was something that could have been sustained for a long time,
"We built an Afghan national army that was very dependent on international air support from command and control and by removing that we've created this horrifying situation."
Mr Stewart also warned of a humanitarian disaster that would result in millions of refugees that would attempt to flee to neighbouring countries.
"We now need to really step up, there are going to be millions of Afghans in horrifying conditions, it's going to be heartbreaking. There will be millions of refugees," he said.
"Iran and Russia will get into the vacuum that we've left behind. We're going to end up with terrorists, but above all, we're going to end up with people in real misery."
He also agreed with Mr Wallace's comments that Afghanistan could become a safe haven for extremists.
"This is going to feel like Iraq and Syria. This is going to be a badly governed space teetering on the edge of civil war and run by an extreme Islamist group."
Gen Richards said the evacuation “is a tacit – explicit, really – admission of failure, of a gross, a dismal failure of geo-strategy and of statecraft".
"I had hoped that we would hear from the government an explanation for why we are in this position and then an explanation of how they are going to avert this disaster. And all we have heard tonight is an admission of failure and a desire to pull people out.”
Philip Ingram, a former intelligence official, said the Taliban had kept their shadow government and military structures intact and had been biding their time for the Nato withdrawal. The precipitous pull-out ordered by US President Joe Biden wasted much of the work that had been done over 20 years.
"We've given a generation the opportunity to go to school, to be educated, to have some freedom, but now we've thrown that back in their faces," he said. "We're leaving and we're leaving it up to them – so we've wasted the last 20 years completely."
British forces were first sent to Afghanistan in 2001 after the September 11 attacks on the United States and played a major role in combat operations until 2014, with 457 British soldiers killed in the country.