David Cameron's tough rules on immigration are taking their toll on UK universities as international students struggle to stump up the fees for entry, according to university and business leaders.

Non-EU students are facing tougher-than-ever visa requirements because of a Conservative pledge to cut net migration by more than a third to 100,000 a year. Depleted student numbers could put some university courses at risk, Bloomberg reports.

"These highly mobile entrepreneurial people will simply go elsewhere," Professor Julius Weinberg, vice-chancellor of Kingston University in southwest London, told Bloomberg via email.

Maddalaine Ansell, chief executive of the University Alliance, which represents 18 colleges, said that Cameron's stance could damage the competitiveness of the UK. "We rely on skills — particularly high-level skills — in order to compete internationally," she said.

Turning away international students could drain £2.3 billion from the economy in tuition fees and living costs, according to data from London First, a business group.