Tony Blair has warned that the return of the Taliban will see “every jihadist group round the world cheering”, as he said that there was now a moral obligation for Western troops to stay until all those eligible are evacuated from Afghanistan.

In a lengthy essay published on his website last night, the former prime minister who ordered British troops to join the US-led invasion said that the hasty withdrawal had been a “tragic, dangerous, unnecessary” decision that undermined the West’s aims. He accused US President Biden of being motivated by “an imbecilic political slogan about ending ‘the forever wars’, as if our engagement in 2021 was remotely comparable to our commitment 20 or even 10 years ago”.

“The abandonment of Afghanistan and its people is tragic, dangerous, unnecessary, not in their interests and not in ours,” he writes. “In the aftermath of the decision to return Afghanistan to the same group from which the carnage of 9/11 arose, and in a manner which seems almost designed to parade our humiliation, the question which allies and enemies alike pose is: has the West lost its strategic will?

“The world is now uncertain of where the West stands because it is so obvious that the decision to withdraw from Afghanistan in this way was driven not by grand strategy but by politics.”

He called on the US and UK to fulfil their obligations to Afghans who had helped them, amid concerns that there may be a window of just a few more days for flights to leave the country. President Biden has given mixed messages about how long he will give the evacuation programme and the UK is unlikely to be able to continue its refugee process once the US military has left.

“We must evacuate and give sanctuary to those to whom we have responsibility – those Afghans who helped us and stood by us and have a right to demand we stand by them,” writes Blair. “There must be no repetition of arbitrary deadlines. We have a moral obligation to keep at it until all those who need to be are evacuated. And we should do so not grudgingly but out of a deep sense of humanity and responsibility.”

Blair said the lack of consultation Britain enjoyed before the US withdrawal showed its power on the world stage was diminishing. “For Britain, out of Europe and suffering the end of the Afghanistan mission by our greatest ally with little or no consultation, we have serious reflection to do,” he states. “We don’t see it yet. But we are at risk of relegation to the second division of global powers. Maybe we don’t mind. But we should at least take the decision deliberatively.”

He said that Russia, China and Iran will “see and take advantage” and that the promises of the West would be seen as “unstable currency”. He also admitted mistakes in the way in which the Afghanistan mission had been handled since 2001.

“We held out the prospect backed by substantial commitment of turning Afghanistan from a failed terror state into a functioning democracy on the mend. It may have been a misplaced ambition, but it was not an ignoble one,” he writes. “There is no doubt that in the years that followed we made mistakes, some serious. But the reaction to our mistakes has been unfortunately further mistakes. Today we are in a mood which seems to regard the bringing of democracy as a utopian delusion and intervention virtually of any sort as a fool’s errand.”

He called on Britain, under its presidency of the G7 group of nations, to commit to coordinating help to the Afghan people “and holding the new regime to account”.