A phone call that Foreign Secretary Dominic Raab was advised to make to Afghanistan’s foreign minister but which was delegated to a junior minister did not take place, it has emerged.

Mr Raab was reportedly “unavailable” when officials in his department suggested he “urgently” contact Hanif Atmar on 13 August to arrange for help to airlift translators out of Afghanistan – two days before the Taliban marched on Kabul.

The responsibility of arranging the call with the Afghan foreign ministry was then handed to a junior minister.

However, it has since been revealed that the phone call never took place.

It was reported on Thursday that Afghanistan’s foreign ministry refused to set up the call with the junior minister, pushing it back to the next day.

This meant crucial time was lost before the Taliban took control of Kabul on Sunday, prompting a desperate scramble to evacuate thousands of Britons and interpreters that is still ongoing.

A Foreign, Commonwealth and Development Office (FCDO) spokesperson said: “Given the rapidly changing situation it was not possible to arrange a call before the Afghan government collapsed.”

And a defence minister told Sky News all government officials are “working their backsides off” to get people out of Kabul.

Mr Raab has been under mounting pressure to resign since he refused to speak to Mr Atmar while holidaying in Crete.

Labour, the Liberal Democrats, the SNP and Plaid Cymru have called for him to step down from his ministerial role and say Prime Minister Boris Johnson should sack him if he does not stand aside himself.

However, Downing Street has said it has “full confidence” in Mr Raab.

The Labour party has set out a list of 18 urgent questions for the foreign secretary to answer about his trip and his department’s handling of the Afghanistan crisis.

The revelation comes amid reports that three of the UK’s most senior civil servants, who are in charge of the departments dealing with the evacuation from Afghanistan, are on holiday.

Sir Philip Barton, Matthew Rycroft and David Williams, who are permanent secretaries at the Foreign Office, Home Office and Ministry of Defence, are all on leave, The Times reported.

A government spokesperson said: “Departments across Whitehall have been working intensively at all levels in the last few days and weeks on the situation in Afghanistan.

“Thanks to these efforts, we have relocated over 2,000 Afghans to the UK since June, evacuated over 400 British nationals and their families on RAF flights since Sunday and established one of the most generous asylum schemes in British history.”

Speaking to Sky News on Friday, Armed Forces Minister James Heappey said “no one phone call would have been decisive in changing the trajectory either for the collapse of the Afghan government, or indeed, for the acceleration of the air lift”.

He added that government officials are “working their backsides off” to evacuate as many people as possible from Kabul.

“I can only tell you what I see in meetings and phone calls that I have all the way through every day, have done for the last week, will do for the next one,” Mr Heappey told Sky News.

“And what I see is from the prime minister, to secretaries of state, to my junior ministerial colleagues around government, to senior servants, all the way down to the brave volunteer civil servants who have gone down to Kabul from the Border Force, from the MoD, from the Foreign Office, is people across Her Majesty’s Government working their backsides off in order to get people out.”

The government said that all Whitehall departments have tried and tested systems for managing when senior officials are on leave or travelling.

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The MoD and Home Office both have two Permanent Secretaries and one is always working while the other is on leave, while at the FCDO there is a designated “acting Permanent Secretary” to cover periods of leave.

Shadow foreign secretary Lisa Nandy condemned the government on the latest news, tweeting: “The Government had 18 months to prepare for this moment.”

Ms Nandy also told Sky News: “It has become incredibly clear that the foreign secretary’s position has become untenable.”

She added that “not picking up the phone to the Afghan foreign minister seems to me to be absolutely shameful on the government’s part”.

Asked by reporters on Thursday morning if he plans to resign over the matter, Mr Raab replied: “No.”

Earlier on Thursday, Defence Secretary Ben Wallace defended Mr Raab, telling Kay Burley that “one phone call is not the reason we are where we are” in terms of the current situation in Afghanistan.

On Thursday, Mr Raab chaired a call of G7 foreign ministers to discuss the crisis, saying afterwards that foreign ministers had agreed each will “engage with partners” to try to secure an “inclusive political settlement” and to enable humanitarian assistance and prevent further loss of life in Afghanistan and to the international community from terrorism.

The government has announced Britain will take up to 20,000 people wanting to exit Afghanistan as part of its resettlement scheme, with 5,000 due to be accepted in the next 12 months.