Britain should avoid further restricting international student numbers or some universities may collapse, a government commissioned report said on Tuesday, after foreign registrations plummeted for next year.

High levels of legal migration have long dominated Britain’s political discourse and were one of the major drivers for the Brexit referendum in 2016.

Along with care staff and low salaried workers, the government of Prime Minister Rishi Sunak has sought to reduce the number of students coming to Britain, including preventing some post-graduate students from bringing family members.

The Migration Advisory Committee, an independent body which gives the government advice, said the number of international postgraduate students paying deposits to study at British universities this September had dropped by 63%, compared with the previous year, after the government put restrictions on education visas.

The report warned that further restrictions on the so-called graduate route, which allows foreign students to work in Britain for up to two years after graduation, would lead to job losses, course closures and a risk “that some institutions would fail”.

Britain boasts some of the most famous and sought after universities in the world, from Oxford and Cambridge to Imperial College London. Business leaders argue that they boost innovation, increase creativity and provide a form of soft power, as many world leaders have studied at British colleges.

The government commissioned the review after concerns that the graduate visa route was being abused. Some British politicians have complained that some students are applying for visas and then claim asylum or overstay.

Esther McVey, a minister in Sunak’s cabinet, said on Monday that some British universities were “selling immigration to international students rather than education”.

A spokesman for Sunak said the government would consider the report and respond. But the spokesman highlighted concerns about the scheme, pointing out that more than 40% of international students using the route were either not working or earning below 15,000 pounds ($18,834) a year after graduation.

The Migration Advisory Committee found there was no evidence of widespread abuse specifically for the graduate route. Students from four countries – India, Nigeria, China and Pakistan – account for 70% of graduate visas.

British business lobby group, the CBI, said British universities were one of the country’s biggest export successes, and with the Migration Advisory Committee saying the system was not being abused “it’s time to put its future beyond doubt and end this period of damaging speculation.”