By Lewis Denison
Any military evacuation presents a desperate situation; rescue people at serious risk, as quickly as possible.
Afghanistan under Taliban rule is no different - thousands are fleeing the Islamist group following its recapture of the country and time is running out in the British military's task of bringing those eligible to the UK.
According to some reports, there could be less than 48 hours remaining before the door on civilian evacuations slams shut.
The UK will "use every hour and day" remaining to get the "maximum number out", says Foreign Secretary Dominic Raab, but what does that mean in reality?
Here we look at the key questions around the UK's evacuation effort.
How many people have been evacuated so far?
So far, although the numbers are constantly growing, the UK has airlifted 10,291 people since it began its Operation Pitting evacuation mission on August 13.
Of those evacuated so far, more than 5,500 them are Afghans and their families.
How quickly is the evacuation effort progressing?
When the evacuation effort began, chaos at Kabul airport meant very few people were able to get inside and reports said a number of flights were being forced to leave without the planned number of passengers.
After Kabul fell to the Taliban, Western forces strengthened their presence there, secured various locations at the airport and, as the UK ambassador said, evacuations were able to gather pace.
When will British and US forces need to start pulling out?
In the past 24 hours, according to the foreign secretary, around 2,000 people have been extracted from Afghanistan.
Evacuations are only able to take place out of Kabul airport, which has seen over 65 flights leave the airfield - nine left in the 24 hours to Tuesday.
Who is still to be evacuated and how many are there?
Defence Secretary Ben Wallace has said the UK is "ruthlessly prioritising ourselves" as it scrambles to complete its evacuation mission.
Those eligible for rescue include British passport holders and Afghans who've helped the UK over the last 20 years, such as interpreters, who fall under the Afghan relocations and assistance policy (Arap).
It's been estimated that around 2,000 people eligible under this policy are still in Afghanistan and are awaiting evacuation by the UK.
The struggle for these Afghans is in both getting to Kabul from wherever else in the country they may be located, and then proving their eligibility to escape.
The UK has said anyone unable to get to the capital could flee the country through Afghanistan's land borders and be processed for resettlement in the UK from neighbouring countries.
The defence secretary says others with special circumstances may also be eligible, such as people who held high profile jobs, LGBTQ advocates, as well as human and feminist rights campaigners.
Why is there a deadline for evacuating civilians?
The deadline for a final withdrawal of Western forces from Afghanistan is August 31 - it's a date set in stone following an agreement between US President Joe Biden and the Taliban.
But the deadline for evacuating civilians is likely to come well before the start of September.
The reason is that military personnel, equipment and infrastructure set up by the West must also be removed by August 31, with the Taliban threatening "consequences" if they are not.
More than 1,000 UK personnel are currently deployed to Kabul and more than 6,000 from the US.
It is not clear how long it will take for British forces to leave, with the foreign secretary saying "planners are working to narrow down the time they need to get out their personnel and equipment".
But with the UK subject to the whims of the US military due to the support it needs, the Britain will need to start leaving as soon as America does - and reports suggest that could happen very soon.
Why are some people being turned away at the airport?
Chaos outside the airport has been blamed, with UK service personnel unable to check people's documents because the sheer volume of people and disruption makes the task even more difficult.
Another reason is that security checks must be carried out on every foreign national hoping to be evacuated by the UK, even if they're eligible.
The defence secretary says security checks are vital, even on those who have worked with the British military, because some haven't done so for more than a decade and could sympathise with the Taliban.
What is the Arap scheme?
Otherwise known as the Afghan Relocations and Assistance Policy, the scheme was launched in April with it already known that Western forces would soon be leaving Afghanistan.
Under the policy, any current or former locally employed staff who are assessed to be under serious threat to life are offered priority relocation to the UK regardless of their employment status, rank or role, or length of time served.
The scheme, however, has been criticised by many as being "too narrow" and when the Taliban's takeover of Afghanistan was complete, a more wide ranging scheme was announced for those ineligible for ARAP.
What about the 20,000 Afghans the UK says it will resettle?
When Kabul fell to the Taliban, Boris Johnson announced that the UK would allow 20,000 Afghans to resettle in the UK in the longer term, on top of the 5,000 he said would be eligible under Arap.
The new Afghan Citizens' Resettlement Scheme will target women, children, and others who have been forced to flee their home or face threats of persecution from the Taliban.
The government said the new route was modelled on the Syrian Vulnerable Persons Resettlement Scheme, which resettled 20,000 Syrian refugees over a seven-year period from 2014 to 2021.