Anti-war campaigners said the UK's mission in Afghanistan had failed and had left a legacy of tens of thousands of civilian deaths as well as a series of unanswered questions.
British troops today handed Camp Bastion over to Afghan forces - bringing to an end their bloody campaign in Helmand province - by lowering the Union Jack for the last time.
It brings to an end a costly chapter in the 13-year campaign, with the vast majority of the UK's 453 casualties losing their lives in the fight against the Taliban insurgency in Helmand.
A series of protests have been held in the UK over recent years demanding the withdrawal of troops amid increasing anger at the rising cost of the conflict in monetary and human terms.
Kate Hudson, general secretary of the Campaign for Nuclear Disarmament (CND), told the Press Association: "When the UK went to war in Afghanistan in 2001, few could have imagined that this bloody conflict would last twice as long as the Second World War.
"Operation Enduring Freedom has certainly endured, though it is not liberty which shall be its legacy. Rather, what will remain is a fractured state mourning tens of thousands of civilians killed in an aimless conflict.
"David Cameron has claimed that the mission in Afghanistan has been accomplished, but which mission is that? Our supposed goals shifted like a weathervane.
"Was our aim the pursuit of those responsible for September 11, in order to bring them to justice? That happened a decade after the invasion, if summary execution can be described as justice, and it didn't even take place in Afghanistan.
"Was our mission regime change? Despite rigged elections and staunch support for the US-installed President Karzai, relations with his government have all but collapsed.
"Meanwhile the Taliban remains in the ascendancy, increasing the rate and the audacity of its attacks, and utilising the mobilising power of a Western imperialist invasion.
"Was our mission controlling the opium trade? Opium production in Afghanistan is higher than it has ever been, now providing around 90% of the world's supply.
"Even women's rights which have been gained over the past decade are being eroded as recent research on the rise of horrific gender-specific violence, including rape and acid-attacks, has made clear."
The CND leader said stability in Afghanistan is a "distant dream", adding: "On all measures, the UK, alongside its US and Nato allies, has failed.
"This should not be surprising: in fact the notion of 'victory' is inconceivable when the goals are unknown and the tool is blunt military force."
Lindsey German, convenor of the Stop The War Coalition, told the Press Association: "The departure of the troops from Afghanistan is welcome, but many questions are unanswered. Why has £20 billion been spent on this conflict while austerity means cuts at home?
"Why has 10 times as much been spent on the military in Afghanistan as has been spent on aid? Why have many thousands died, including 447 British troops?
"How many advisers and military support will be left in Afghanistan following the withdrawal? What was the point of this war which has gone on longer than the First and Second World Wars combined?
"It has not brought stability, peace or democracy to the country, nor has it made Britain a safer place."