The UK’s Independent Commission for Aid Impact found that money sent to the country before it fell to the Taliban in August last year was spent on plans for nation-building and security that were not “realistic.”

Around £252 million ($305 million) was sent to Afghanistan in aid for police operations, as part of more than £3.5 billion in aid sent in total, which, the ICAI said, had funded “police corruption and brutality, including extortion, arbitrary detention, torture, and extrajudicial killings.”

Theft of equipment purchased with British aid money was common, and police forces would routinely register “ghost officers” on their payrolls. There were also frequent reports of police officials using their positions of authority to sexually abuse young boys.

The ICAI’s report noted that efforts to block spending on police when the issues came to light were opposed at the “highest levels of the UK government.”

The ICAI added that a UK decision to transfer funds via the Afghan government had compounded corruption, denying regional authorities access to much-needed aid, but British schemes for women and girls focused on matters such as education and early motherhood had been relatively successful.

Hugh Bayley, the commissioner of the ICAI, said: “The international evacuation from Afghanistan marked the end of one of the most ambitious undertakings ever pursued by UK aid.

“It’s clear that the remarkable efforts by those working on the UK aid program made a significant difference to many people in Afghanistan, including women and girls.

“However, the way the UK pursued its primary objective of building a viable Afghan state contained key flaws that contributed to its ultimate failure, and there are questions around the appropriateness of using UK aid to fund Afghan counter-insurgency operations.

“It’s not clear if the gains made by the UK’s aid program, in improving literacy and reducing child mortality for example, will last under Taliban rule, and there are lessons that must be learned and used to guide future stabilization and state-building initiatives,” he added.

British Conservative MP Richard Bacon told The Telegraph: “Aid workers in Afghanistan are to be commended on the effective work they have delivered through individual programs.

“However, the long-term success of the UK aid program in Afghanistan is in doubt as a result of the failure to secure a viable Afghan state.

“The independent aid watchdog, ICAI, rates the UK’s development assistance to Afghanistan as unsatisfactory in most areas.

“It has found that decisions to fund police or other security agencies were ill-conceived. The ICAI states that in highly fragile contexts such as this, ministers must consider the prospects of viable political settlements in the sustained belief of a successful transition out of conflict.

“This review demonstrates that individual UK aid programming can succeed, but ministers must work out their priorities and direct UK aid to where it counts,” he added.

A British Foreign Office spokesman told The Telegraph: “UK aid improved health; increased school enrolment; provided humanitarian support to the most vulnerable; and led the way in clearing landmines and other unexploded munitions across the country.

“We welcome the commission’s report and will provide a formal response in due course.”