The UK’s evacuation flights from Afghanistan may have to stop this week after Boris Johnson failed to secure an extension to a US deadline for all western forces to leave.

The Guardian newspaper reported late on Tuesday that the last Royal Air Force aircraft carrying Afghans to safety from Kabul airport could even be in the next “24 to 36 hours”.

But defence sources described the timeline as speculative and said it was not “set in stone”.

Still, a team of more than 1,000 British troops and diplomats running Britain’s evacuation mission on the ground will need a period of time to pack up their equipment and depart ahead of the final US exit date of 31 August – next Tuesday.

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It means that evacuation flights for Afghan civilians desperate to flee the country after a shock Taliban takeover will have to stop at least a number of days before then.

Ministers have made it clear that the UK cannot remain at the airport without the presence of a 6,000-strong US force, which has been providing security and is also running the airfield.

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Yet, officials have also been careful not to talk publicly about exact plans for the final drawdown, concerned about the risk of triggering a new rush of men, women and children to the airport to try to access flights as soon as they realise when they will stop.

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Last weekend several people were crushed to death in chaotic scenes outside the gates.

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Then again, Britain’s prime minister and other allies failed to persuade US President Joe Biden to delay the US exit deadline during a virtual G7 meeting of global powers on Tuesday – so it is no secret for any Afghans wanting to be evacuated that their time is limited.

The Washington Post reported on Tuesday that US troops have started to pull out of Kabul already.

Even as the end of the evacuation looms, the tempo of flights and the number of people being airlifted to safety remains high.

More than 9,200 people – British nationals as well as Afghans who have worked with British troops and diplomats over the past two decades but are now in danger – have been flown to safety in the UK since 13 August as part of what has been dubbed Operation Pitting.

The Ministry of Defence said in a statement about the mission: “The evacuation process will run as long as the security situation allows in joint coordination with our US partners. No firm date has yet been set for the end of evacuation flights.”