Retired General Richard Dannatt, the former chief of the General Staff, and other senior leaders of the campaign in Afghanistan, said the resettlement program for interpreters and other staff needed to act with more "generosity and urgency."

"Too many of our interpreters have unreasonably been rejected," they said in a letter to Prime Minister Boris Johnson that was published on Wednesday.

"We urge the government to review the policy immediately. Only those constituting a national, security threat should be excluded."

The UK has a "moral obligation" to resettle people who risked their lives to help British troops, and failure to do so will damage the country's reputation abroad, Dannatt said in an interview with the BBC.

Among those currently ineligible for resettlement are Afghans who were dismissed for minor infractions, such as a man who took an unauthorised day of leave to visit his sick mother, Dannatt said.

Expanding the program would allow about 4000 more Afghan employees and their families to move to the UK, in addition to the 3000 who have already been resettled, he said.

"We are also gravely concerned for Afghan staff who provided essential support to us but who are ineligible for relocation because they did not work in an 'exposed role' or were contracted through third parties," the former commanders wrote. "The Taliban make no such distinction."

At the peak of the post-2001 deployment there were almost 10,000 British troops in Afghanistan, mostly in Helmand province in the south. Britain ended combat operations in 2014, but about 750 troops remain in the country to train Afghan forces.

US and other NATO troops are ending a deployment launched against al-Qaeda and Taliban forces in the wake of the September 11 attacks.

Australian Associated Press