Efforts by universities to boost the number of foreign students – a core strategy of some of Britain’s most elite institutions – have been branded “unsustainable” by a body charged with maintaining standards in higher education.

The news throws into question the viability of a valuable source of income for the UK. It is second only to the US as a magnet for bright overseas students – many of whom stay in the country after finishing their studies to become top talent in the labour market.