A-level results will be the "most unfair in a generation", headteachers have warned, after changes to the appeals process that may result in students missing out on places at elite universities.

Leading heads of both private and state schools said that students appealing exam results face “the most chaotic and unfair year in a generation”.

In May this year, Ofqual, the exam boards regulator, said it would only allow re-marking if there were "clear errors".

In a major clampdown on exam appeals, Ofqual said it would press ahead with a tougher system that will make it harder for some pupils to get a “second bite of the cherry”.