Dominic Raab has flown to Qatar to hold talks about the Government’s “top priority” of safely evacuating British nationals and Afghan interpreters from Taliban-controlled Afghanistan.

The Foreign Secretary’s trip began hours after he faced a grilling from MPs about the evacuation effort from Kabul airport, where he was asked about a Foreign Office document from July which suggested the Taliban could advance rapidly across Afghanistan.

The Prime Minister is meanwhile expected to visit troops in the south east of England who helped with the evacuation from Kabul.

A statement from the Foreign Office said Mr Raab’s “immediate priority” is to help UK nationals and Afghans who supported British forces to travel to the UK.

The Foreign Secretary will meet the Amir of Qatar, Sheikh Tamim bin Hamad Al Thani, and the deputy prime minister and foreign minister Sheikh Mohammed bin Abdulrahman Al Thani during his visit to the Persian Gulf state.

Before heading to the airport, Mr Raab spoke to the Indian foreign minister, Dr Subrahmanyam Jaishankar, and thanked him for helping to secure a UN Security Council Resolution on Afghanistan.

The Foreign Office said Mr Raab will discuss the Government’s “four key priorities for Afghanistan” while in Doha, which include “preventing Afghanistan becoming a haven for terrorists, responding to the humanitarian plight, safeguarding regional stability, and holding the Taliban to account on human rights”.

As Mr Raab visits Doha, Foreign Office minister Lord Ahmad of Wimbledon will travel to Tajikistan to discuss the safe passage of those fleeing there from neighbouring Afghanistan.

On Wednesday, Mr Raab told the Foreign Affairs Committee that the number of British nationals still in Afghanistan were in the “low hundreds” but he could not give a “definitive answer” of how many people in Afghanistan who would be eligible for settlement in the UK under existing schemes have been “left behind”.

Mr Raab faced sustained questioning from MPs on how the UK failed to predict the speed at which the Afghan government would fall to the Taliban, which seized Kabul on August 15.

He told them: “The central assessment that we were operating to, and it was certainly backed up by the 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’d see a steady deterioration from that point and it was unlikely Kabul would fall this year.”

A Foreign Office document called a principal risk register, published on July 22, appeared to warn Afghanistan could fall to the Taliban much sooner than the UK had previously predicted.

The document, seen by the Guardian, said: “Peace talks are stalled and US Nato withdrawal is resulting in rapid Taliban advances. This could lead to: fall of cities, collapse of security forces, Taliban return to power, mass displacement and significant humanitarian need. The embassy may need to close if security deteriorates.”

However, a Foreign Office spokesman said it was “wrong and misleading” to suggest the document was “at odds with our detailed assessments of the situation in Afghanistan or our public position throughout the crisis”.

They added: “The July document makes clear that our central planning assumption at the time was that the peace process in Afghanistan would run for up to a further six months.”

Mr Raab was also pressed by MPs about his holiday to Crete in mid-August as the Taliban surrounded Kabul, but he refused to offer further details, labelling the questions a “fishing expedition”.

As Mr Raab holds safe passage talks in Doha, Boris Johnson is expected to visit a military base in the South East on Thursday and meet troops involved in the evacuation of Kabul airport.

The Prime Minister is returning from a four-day trip to the West Country which began on Sunday.

His official spokesman declined to describe it as a holiday, instead insisting Mr Johnson was “continuing to work” away from the office.