Ministers' controversial diplomas for teenagers were hit by yet another brickbat when they were branded by a think-tank as qualifications for "refugees" from tougher academic exams.

The report from the Nuffield Foundation, one of Britain's leading independent authorities on public policy, also raised fears that diplomas would be "unable to establish a high-status reputation". It cuts to the heart of fears about diplomas in business and the education industry: that more able pupils will happily continue doing GCSEs and A-levels, and ignore diplomas - turning them into a low-prestige qualification for poorly-performing pupils.