Peter Hamilton, headmaster of The Haberdashers’ Aske’s Boys’ School in Hertfordshire, believes that selective higher education institutions will follow the University of Cambridge’s lead and introduce written admissions tests.

It comes following the government’s decision to decouple A levels and AS levels despite repeated warnings from school and university leaders alike.

Universities often use AS levels as guide to predict students’ performance in Year 12, but Mr Hamilton believes that the government’s changes will lead to university admissions tutors having to rely on internal school assessment of “varying quality”, according to TES’ sister publication, Times Higher Education.

“There’s a train crash waiting to happen with this lottery that we are going into; the decoupling of A levels will help not one jot,” the headmaster told an event on admissions organised by the Westminster Higher Education Forum. “There will be mistakes made because there is unreliability built into the system.”

Universities will be forced to pick students holding a “ragtag mixed bag” of qualifications as a result of the government’s exam reforms, Mr Hamilton warned.

And he added: “I would prophesise there is going to be rapid growth in selective universities who will set their own entrance tests…if you look at the scenario I’ve been painting, what other choice might you have if you are selecting rather than recruiting?”

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