British Foreign Secretary Dominic Raab said he will travel to Afghanistan's neighbours on Wednesday, as he defended the UK government's approach to the country following weeks of scathing criticism from across the political spectrum.

During nearly two hours of questions from lawmakers, Raab insisted Britain had prepared for all eventualities ahead of last month's Taliban takeover and would continue trying to help those fleeing the new regime in Kabul.

Ahead of visiting the unspecified countries to discuss allowing vulnerable Afghans entry and onward travel to the UK, he said the Foreign Office was dispatching 15-person "rapid deployment teams" to continue London's evacuation efforts.

Britain has opened talks with the Taliban over the safe passage of its remaining nationals and allies out of Afghanistan and dispatched senior civil servant Simon Gass to meet with Taliban representatives in Doha.

It is the first publicly disclosed diplomacy between London and the Taliban since Britain joined the United States in the mammoth airlift of more than 100,000 people out of the country after the Afghan military's capitulation. 

"I'm going to the region tonight to test the accessibility of these arrangements," Raab told the cross-party panel of MPs grilling him at a special watchdog hearing.

"We've got to keep those borders open. And I think part of that is giving those third countries arrangements that they can feel confident in, perhaps support as well."

He is expected to make an initial stop in Doha, which has proved a key hub for Taliban officials.

Challenging

Britain's top diplomat, who has faced calls to resign after going on holiday ahead of the mid-August Taliban takeover, staunchly defended both his and the government's conduct during the chaotic evacuations of British nationals and vulnerable Afghans.

More than 8,000 people potentially eligible to leave have been left stranded after the last UK military flight left Afghanistan on Saturday.

Current and former officials have condemned the government, suggesting many more could have been rescued in recent months and hit out at faulty phone and email systems set up to process evacuation applicants.

However, Raab called it "the most challenging evacuation of its kind in memory" and noted more than 15,000 people had been evacuated during the last two weeks.

That included 287 journalists, 65 women's rights activists, 37 "extremely vulnerable" individuals and dozens of former officials.

Raab said the government began planning earlier this summer to shift embassy operations to Kabul airport if required and speeding up the relocation of former Afghan staff. 

"We started planning in June for the contingency of an evacuation and the full drawdown of the embassy," Raab said, as he faced accusations of incompetence and criticism for taking an August luxury holiday in Crete.

"I've been clear with the benefit of hindsight I wouldn't have gone away at all," he added, while repeatedly refusing to detail exactly when he headed to the beach. 

Vital support

Earlier on Wednesday, Prime Minister Boris Johnson said Britain owed "an immense debt" to Afghans who worked with NATO forces as his government announced "vital support" for those resettling in the UK.

They will be given immediate indefinite leave to remain, while £15 million ($21 million, 17 million euros) would be provided for additional school places and to support access to the health service.

"We owe an immense debt to those who worked with the armed forces in Afghanistan and I am determined that we give them and their families the support they need to rebuild their lives here in the UK," Johnson said of the so-called "Operation Warm Welcome" measures.

Britain also has a resettlement scheme for Afghans fleeing from their home country, with about 5,000 expected this year and 20,000 in total.

Resettlement minister Victoria Atkins on Wednesday told Sky News that it was not yet decided whether those arriving under this programme would get indefinite leave to remain.