The UK's withdrawal from Afghanistan last year was a "disaster" and a "betrayal" that will damage the nation's interests for years, an inquiry by MPs has found.
The Foreign Affairs Committee said there had been "systemic failures" of intelligence, diplomacy and planning.
Chairman Tom Tugendhat said there had been a failure to lead "at a time when lives were quite literally being lost".
The UK government said "intensive planning" went into the withdrawal.
A spokesperson for the Foreign, Commonwealth and Development Office (FCDO) defended its handling of the withdrawal and said it would review and respond to the committee's findings.
The cross-party MPs who carried out the inquiry said "mismanagement" of the evacuation as the Taliban quickly took over the country "likely cost lives".
They added they had lost confidence in the department's top civil servant, Sir Philip Barton, and urged him to consider his position.
The report said the fact Sir Philip, the then-Foreign Secretary Dominic Raab and Prime Minister Boris Johnson were all on leave when the Taliban took Afghanistan's capital, Kabul, "marks a fundamental lack of seriousness, grip or leadership at a time of national emergency".
Mr Tugendhat told BBC Radio 4's Today programme: "It's a very clear criticism of the failure to plan, the failure to prepare, and the failure to lead at a moment of extraordinary national emergency, at a time when lives were quite literally being lost, at a time when every decision was fraught with risk, and highly contentious, and needed to be made very quickly by people who had the authority to do so."
The "fundamental failure" was one of leadership, the Conservative MP added.
Labour shadow foreign secretary David Lammy said the report "highlights the scale of the government's incompetence, laziness and mishandling" of the withdrawal.
"The Conservative government has badly let down Britain's reputation on the global stage and those responsible for this calamity should be held accountable," he said.
The PM's official spokesman said Mr Johnson retained full confidence in Sir Philip.
Asked why he remained the right person to head the FCDO, the spokesman said: "He has significant experience in that field and a number of changes have already been made."
The spokesman also said Mr Johnson did not regret making Mr Raab deputy prime minister after the evacuation.
A coalition of international forces - led by the US - completed their withdrawal from Afghanistan on 30 August 2021, marking the end of the 20-year campaign in the country.
US-led forces went into Afghanistan in 2001, removing the Taliban from power in the wake of the 9/11 attacks, which were blamed on al-Qaeda - a militant jihadist group.
The UK sent forces but ended its combat operations in 2014, leaving hundreds of troops to help train the Afghan government's army.
In February 2020, a withdrawal deal was signed by the Taliban and the US under former President Donald Trump and a year later his successor, Joe Biden, honoured the agreement.
As the US pulled out troops and reduced military support for the Afghan army, the Taliban made rapid territorial gains, reclaiming control of the whole country by mid-August.
A reminder of the horror and shame
The report brings back the sense of horror and, for some, shame generated by last August's traumatic evacuation from Kabul.
It was always inevitable that ministers and senior officials were going to be lambasted. During the committee's hearings, MPs expressed their dismay that the Foreign Office's top civil servant hadn't seen fit to return from holiday until the civilian evacuation was over.
And it was clear that they found some of the answers they received evasive and unconvincing.
Some will argue that the speed of the Taliban's takeover of the country could not have been anticipated and made planning for such a complex evacuation impossible without causing widespread panic.
It's not an argument that cuts much ice with the MPs. They say there was plenty of time to make plans and that what happened was a betrayal that will haunt the UK's international reputation for years.
In September 2021, the committee launched an inquiry to consider the role of the FCDO in the build-up to, during and after the withdrawal.
The committee published its findings on Tuesday in a report, which "identified systemic failures of intelligence, diplomacy, planning and preparation - many of which were due, at least in part, to the Foreign Office".
In key findings, the report said:
On planning for withdrawal
- The government "failed effectively to shape or respond to" the US's decision to withdraw from Afghanistan, which was known since February 2020
- The FCDO "failed to make the necessary preparations for withdrawal" by laying the groundwork for an evacuation with third countries
- There was a "total absence of a plan for evacuating Afghans who supported the UK mission, without being directly employed by the UK government"
On the evacuation
- This "mismanagement" of the evacuation in a crucial period "likely cost hundreds of people their chance to leave the country, and as a result likely cost lives"
- The fact that the FCDO's top civil servant did not return from leave until the civilian evacuation was over "is difficult to understand and impossible to excuse"
- The FCDO gave the committee answers that were "often deliberately misleading" in response to questions about the decision to evacuate animals looked after by the charity Nowzad
On the future relationship with Afghanistan
- Attempts to isolate the Taliban "may only worsen the situation for the Afghan people, reduce the UK's influence, and leave a vacuum to be filled by powers such as China"
- The primary UK policy goal in Afghanistan "should be to reduce the impact of the humanitarian disaster unleashed by the international withdrawal"
- The withdrawal has "serious implications for British security and has "heightened the terror threat" from Afghanistan
Amy Richards, director of the charity Global Witness, said no-one who was involved in the withdrawal would be surprised by the "chaos, confusion and a total lack of leadership" described in the report.
However, she said it failed to address a "continued failure" of the UK to meet its responsibilities, arguing government refugee schemes "have barely got off the ground".
"As life gets harder for those in Afghanistan, Britain is further pulling up the drawbridge and letting down those who carried out brave acts of solidarity on our behalf over many years. We should be utterly ashamed by this," Ms Richards said.
The UK airlifted about 15,000 Afghans and British nationals out of Kabul as the Taliban took control of the country. Thousands of staff from across the UK government and partners supported the evacuation effort.
An FCDO spokesperson said: "This was the biggest UK mission of its kind in generations and followed months of intensive planning and collaboration between UK government departments.
"We are still working hard to assist the people of Afghanistan, having already helped over 4,600 individuals to leave the country since the end of the military evacuation.
"We carried out a thorough review to learn lessons from our withdrawal from Afghanistan, and have drawn on many of the findings in our response to the conflict in Ukraine - including introducing new systems for managing correspondence and increasing senior oversight of our operational and diplomatic response."