Mr Wallace, who previously served in the Scots Guards regiment of the British Army, struggled to hold back tears as he spoke of the 20 years of sacrifice to then see Kabul fall to the Taliban.
British troops are racing against the clock to get remaining UK nationals and their local allies out of Afghanistan following the dramatic fall of the country’s Western-backed government.
Around 4,000 British nationals and eligible Afghans are thought to be in the city and in need of evacuation.
The first flight carrying British nationals as part of an operation to evacuate people from Afghanistan arrived in the UK last on Sunday night. Embassy staff were among the people who arrived at RAF Brize Norton.
Last night the first flight of British Nationals and Embassy Staff arrived at RAF Brize Norton as part of Op PITTING.
The UK Armed Forces are supporting the evacuation of British Nationals and those eligible for relocation under the Afghan Relocation and Assistance Program. pic.twitter.com/IyGNIMEaD0
— Ministry of Defence 🇬🇧 (@DefenceHQ) August 16, 2021
Mr Wallace began to choke up on Monday as he spoke to LBC.
“We are not doing any diplomatic functions, we are simply there to process all those British passport holders and those we have obligations to.
“Our men and women of the armed forces are risking their lives in doing that but that is the right thing to do.
“They have risked their lives for the last twenty years and at the very least our obligation has to be to get as many people as possible through the pipeline.
“It’s a really deep part of regret for me … look, some people won’t get back. Some people won’t get back and we will have to do our best in third countries to process those people.”
Asked why he felt the situation “so personally”, Mr Wallace replied: “Because I’m a soldier… because it’s sad and the West has done what it’s done, we have to do our very best to get people out and stand by our obligations and 20 years of sacrifice is what it is.”
Following a meeting of the Government’s Cobra emergencies committee, Boris Johnson his priority was to get UK nationals and Afghans who had worked with them out of the country “as fast as we can”.
“We are going to get as many as we can out in the next few days,” he said.
When the Operation Pitting rescue operation, involving 600 troops, was announced at the end of last week, the defence secretary said it could carry on through the rest of the month.
But the speed of the Taliban advance suggests that there may only be a short window of a few days to get people out.
In a sign of the desperate situation the British ambassador Sir Laurie Bristow was said to be helping the small team of diplomats still in the country to process the applications of those hoping to leave.
There was particular concern for the safety of Afghans who worked with British forces when they were in the country as interpreters and other roles amid fears of reprisals if they fall into the hands of the insurgents.
The Taliban insisted that they were seeking a peaceful takeover of power and were prepared to offer an amnesty to those who had worked with the Afghan government or with foreign governments.
However those assurances were being treated with deep scepticism by many British MPs amid reports of threats to those who remain and their families.
Labour called on the Government to urgently expand the resettlement scheme for Afghans to ensure that none were left behind.
Shadow foreign secretary Lisa Nandy said: “Some of them have already been killed, others have received threats to themselves and their families.
“We have an obligation as a country to make sure that they are safe.”