Dominic Raab has admitted that Kabul was not expected to fall to the control of the Taliban until next year.
The Foreign Secretary said the intelligence assessment was that there would be a "steady deterioration" once US and UK troops withdrew from Afghanistan at the end of August.
Instead, Taliban militants stunned Western forces by sweeping rapidly through the country, seizing control of the capital on August 15.
Mr Raab, who has faced criticism for being on a summer break in Crete when Kabul fell, was challenged over the UK's withdrawal from Afghanistan by the Commons Foreign Affairs Committee.
Tory Committee chairman Tom Tugendhat confronted Mr Raab with a departmental report from June 22 which warned of serious risk of the country's collapse.
In a fiery hearing, the Foreign Secretary admitted he had no idea how many Brits are left in Afghanistan - and refused to say when he started his beach holiday.
But he also revealed he will fly to the "region" immediately after today's hearing.
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While destinations are being kept under wraps, Mr Raab is expected to fly to Doha, Qatar, where UK officials have been meeting "senior Taliban representatives" to plead safe passage for those fleeing Afghanistan.
The Foreign Secretary also appeared to indicate he could visit Pakistan on the trip.
Mr Raab tried to defend the handling of the UK's withdrawal by pointing to intelligence suggesting that the Taliban would not seize control until next year.
He told MPs: "The central assessment that we were offered and it was certainly backed up by both JIC (Joint Intelligence Committee) and the military is that the most likely, the central proposition was that given the troop withdrawal by the end of August, you would see a steady deterioration from that point and that it was unlikely Kabul would fall this year."
Mr Raab insisted there had been contingency planning and the view was "widely shared" by NATO allies.
This assessment remained "until late", he said, adding: "The planning for military withdrawal began in April but the contingency plan was also there for a more rapid deterioration."
But Mr Tugendhat read out an internal risk report from the Foreign Office in June, which set out the serious security threats.
It comes amid a Whitehall blame game over the handling of the crisis, with Mr Raab appearing to point the finger at the intelligence he was given.
The last US troops left Afghanistan on Tuesday morning local time after a 20-year campaign by the American and British military.
The UK and the US were forced to deliver a chaotic mass evacuation following the Taliban's rapid advance - but hundreds of British nationals and vulnerable Afghans were left behind.
Pressed on whether “thousands” of eligible Afghans had been left behind, Mr Raab replied: "I’m not confident with precision to give you a set number, but I am confident the Prime Minister is right that we’ve got the overwhelming majority out."
He added: "Any number that we haven’t got out because of the evacuation, because of the situation, is too many."
Mr Raab said he would be visiting the region around Afghanistan imminently but did not specify where or who he would be meeting.
"We're always very careful about signalling travel movements because of the security implications," he said.
"But I can tell you I'm leaving after this committee to go to the region."
Questioned by Labour’s Chris Bryant, Mr Raab repeatedly refused to reveal the start date of his five-star beach holiday in Crete.
Mr Bryant had asked if Mr Raab - who only returned from his break after Kabul fell - left before or after August 11.
Complaining he had answered questions “continuously”, he told Mr Bryant: "I’m not going to start adding to frankly the fishing expedition beyond the facts I’ve articulated in a fulsome statement."
He said he had engaged in “all of the COBRA meetings” and “directed the emergency response team directly” but admitted: “With the benefit of hindsight I wouldn’t have gone away at all.”
