The Armed Forces Minister has said the "imminent and lethal" threat of an ISIS attack at Kabul airport will mean more people "won't get out" of Afghanistan.
James Heappey said an attack from ISIS-K could happen in Kabul within "hours" and told Forces News this will mean fewer people will be evacuated than "we would have hoped for".
"We're looking at what other routes there might be to get people into the airport, but very obviously we're not going to advertise what those routes might be because those routes would become a target in their own right," he said.
"People should expect to hear from us, and we will make sure that we explain to them what the plan is.
"But make no mistake, whatever contingencies we're able to develop, they won't be a like-for-like replacement of what we've lost by having to advise people to stay away."
Watch: Government looking at alternative options for evacuations.
Personnel from 16 Air Assault Brigade are currently supporting the evacuation of British nationals and former British staff in the Afghanistan.
However, if the 31 August withdrawal deadline remains in place, British troops will have to leave before the US and hand over tasks and responsibilities to other nations.
Mr Heappey refused to comment on whether today would be the last day of evacuation flights from Kabul airport.
He did confirm "all 11 flights that were planned for this 24-hour period were evacuation flights", but also said "bits of the military presence" in Kabul "are starting to be backloaded".
"What we would, I think, envisage, is that there may be an opportunity to get processing again at volume if the threat somehow subsides," he said.
Watch: Afghanistan – who are ISIS-K?
"But I don't want to offer that with any sort of certainty."
When asked if those looking to leave Afghanistan are faced with either facing the threat of an ISIS attack at the airport, or the Taliban, Mr Heappey said "regrettably, that is the case".
"I think that's why you're seeing, despite the advice changing from the US, UK, Australia overnight, thousands of people [are] still outside the airport."
Earlier this week, US President Joe Biden said "every day [the US are] on the ground" in Afghanistan "is another day we know that ISIS-K is seeking to target the airport, attack both US and allied forces, and innocent civilians".
And Sajjan Gohel, the international security director at the Asia-Pacific Foundation think-tank, told Forces News the group was a threat both inside Afghanistan "and, potentially, if left unchecked," internationally.