Immigration remains one of Britain's most politically sensitive issues, and Prime Minister Keir Starmer's government has sought to show it is tightening the system as the populist Reform UK party gains ground in opinion polls.
The interior ministry, which is set to block study visas for nationals from Afghanistan, Cameroon, Myanmar and Sudan, said on Tuesday asylum applications by students from these countries had jumped more than fivefold between 2021 and 2025.
It also said claims by Afghans on work visas were now outstripping the number of visas issued.
"Britain will always provide refuge to people fleeing war and persecution, but our visa system must not be abused," interior minister Shabana Mahmood said in a statement.
"That is why I am taking the unprecedented decision to refuse visas for those nationals seeking to exploit our generosity."
Asylum claims made after entering on legal visas have more than trebled since 2021 and accounted for 39 per cent of the 100,000 people who applied last year.
It said that nearly 16,000 nationals from the four listed countries were currently being supported at public expense, including more than 6000 in hotels, adding to pressure over the cost of asylum accommodation, which it put at stg4 billion ($A7.6 billion) a year.
The changes would take effect on March 26, the government said, adding that it intended to create new capped "safe and legal routes" once the asylum system stabilises.
Britain has granted sanctuary to more than 37,000 Afghans through resettlement schemes since 2021 and issued about 190,000 humanitarian visas last year.
It said it had secured co-operation from Angola, Namibia and the Democratic Republic of Congo on returns, after warning in November that their nationals risked losing access to UK visas.
Starmer has previously said that Britain's asylum rules were more permissive compared with parts of Europe and acted as a "pull factor" for people seeking to reach the country.
