The government will halt visa routes for nationals from four countries who the home secretary says have "abused" the UK's generosity.
An emergency brake is being placed on study visas for people from Afghanistan, Cameroon, Myanmar and Sudan, while work visas have also been stopped for Afghans.
It's the first time such visa bans have been implemented by the UK government.
Shabana Mahmood claimed a growing number of migrants from these countries are using legal migration routes as a backdoor for claiming asylum.
According to Home Office figures, 39% of the 100,000 who claimed asylum in 2025 did so after arriving via a legal migration route.
A spike in asylum applications between 2021 and September last year was dominated by students from Afghanistan, Cameroon, Myanmar, and Sudan.
Ms Mahmood said: "Britain will always provide refuge to people fleeing war and persecution, but our visa system must not be abused. That is why I am taking the unprecedented decision to refuse visas for those nationals seeking to exploit our generosity."
The bans will be officially introduced on Thursday, when Ms Mahmood will lay out measures to toughen up the asylum system.
They would include asylum seekers having to have their refugee status reviewed every two-and-a-half years.
Refugees whose countries are deemed safe will also be expected to return home.
Read more on Sky News
How UK and Denmark's immigration policies compare
Ms Mahmood's tougher approach doesn't sit comfortably with many Labour MPs, but she has warned a failure to address the public's concerns about immigration will lead to a right-wing government.
But the government is also coming under pressure from its left flank, after the Greens won the year's first Westminster by-election.
Ms Mahmood has argued the level of illegal immigration is "creating division within communities across the country", risking the erosion of public support for the asylum system entirely.
The government has committed to ending the use of hotels to house asylum seekers by the next election, though its plans for using old military sites are also proving unpopular.
(c) Sky News 2026: UK to impose 'unprecedented' visa ban in asylum crackdown
Greens overtake Labour in sensational poll
UK will deploy HMS Dragon in Cyprus, Sir Keir Starmer confirms
Iran war leaves forecast for low UK inflation not worth the paper it was written on
Ferry scandal fall-out sees Ardrossan harbour buy-up and new contracts for beleaguered shipyard
