Most British soldiers have been pulled out of Afghanistan, ending Britain’s official role in a two-decades long conflict even as the Taliban are gaining ground and amid fears the departure of foreign soldiers could lead to civil war.

“All British troops assigned to Nato’s mission in Afghanistan are now returning home,” Prime Minister Boris Johnson told parliament, praising what British forces had achieved while at the same time acknowledging the “perils” facing Afghanistan. “For obvious reasons, I will not disclose the timetable of our departure, though I can tell the house (parliament) that most of our personnel have already left,” Boris said.

British forces were first deployed to Afghanistan in 2001 following the September 11 attacks on the US and played a major role in combat operations until 2014. A total of 457 British soldiers were killed in the country.

Nato, of which Britain is a member, said in April that its troops would begin withdrawing in co-ordination with a decision by President Joe Biden to pull US troops out by September 11.

Violence has raged throughout Afghanistan in the weeks since then.

The US last week abandoned Bagram air base, the longtime staging ground for US military operations in the country, effectively ending America’s longest war. The Pentagon says the withdrawal of US forces is 90 per cent complete.

Boris said he did not underestimate the challenges facing Afghanistan, adding the government would continue to provide development assistance. “I hope no one will leap to the false conclusion that the withdrawal of our forces somehow means the end of Britain’s commitment to Afghanistan, we are not about to turn away, nor are we under any illusions about the perils of today's situation and what might lie ahead,” Boris said.

Britain’s ministry of defence said a small number of troops will remain to protect diplomats.

Nick Carter, who as chief of the defence staff is the head of the armed forces, said there is the possibility that Afghanistan could be on a path to civil war as American and other foreign troops leave.

Recent news from Afghanistan has been “pretty grim” and it is “plausible” that the country’s state would collapse without foreign troops there, he told reporters.

Afghanistan could see a situation like the country’s 1990s civil war “where you would see a culture of warlordism and you might see some of the important institutions like security forces fracturing along ethnic, or for that matter, tribal lines”, he said.

“If that were to happen, I guess the Taliban would control part of the country..”

Boris said Britain could be proud of its role in Afghanistan. The US-led coalition supported the Northern Alliance in toppling the Taliban government, accused by Washington of harbouring al Qaida after the September 11 attacks. He said there have been improvements in women’s rights, and education, and there has not been a militant attack in the West launched from Afghanistan since the invasion.