More than 70 per cent of 1,400 15 and 16-year-olds surveyed were expecting five or more GCSE grades A*-C, even though only 27 per cent of students at the schools surveyed actually achieved that standard. Nationally, 47.9 per cent of pupils get five GCSEs at grade C or better.

However, FOCUS, the training and enterprise council for central London, which conducted the survey, says getting lower grades than expected did not need to be a barrier to future success, even if it meant students could not go on to A-level.

It said teenagerswere badly informed about the diverse range of post-16 options, many of which allowed them to learn and earn at the same time.

Of those surveyed who had decided on a career, more than half were aiming at professional or managerial occupations via the traditional A-level route. But few were aware of paid, work-based alternatives, including Youth Credits, National Traineeships and Modern Apprenticeships.

Jude Belsham, senior researcher at FOCUS, said: “Whilst every student should be encouraged to aim high, they must remain realistic. The overwhelming majority of young people are opting for a sixth-form or college place - which, for some, may be the wrong choice.”