Dr Pamela Robinson, of the Centre for Education and Employment Research at Brunel University, warned of an increasingly two-tier education system, with the best opportunities, from nursery to university level, going to the better-off children.

She said university tuition fees would do little to put off students from poor backgrounds because most had been filtered out of the system even before they took A-levels.

New figures from the Universities and Colleges Admissions Service for the study show working-class students get into university on lower A-level grades than their middle-class counterparts.

Dr Robinson said the figures showed universities were not discriminating against working-class students. But she acknowledged there was no evidence to show which institutions or courses working-class teenagers attended - leading to fears that elite institutions may have intakes heavily biased towards the middle classes.

A draft report prepared by Dr Robinson and fellow researcher Paul White, argues that the education system acts as a filter, with primary and pre-school education the crucial factor in determining who goes on to higher education.

The report says: “The social-class bias that exists in the post-compulsory education system is largely inherited from the compulsory education system, a consequence of decisions taken when the children were 7 and 11 rather than 16 or 18.

“Only by fundamentally altering the way we teach children in the pre-secondary sectors will they have the chance drastically to change the long-term social-class distribution of higher education.”

Dr Robinson’s study of A-levels show 60 per cent of people with two or more A-levels stay in education regardless of social class.

But the vast majority of working-class youngsters do not get as far as A-level - students from blue-colla r backgrounds are three times less likely to have gained two or more A-levels and five times less likely to go to university than their middle-class classmates.

Dr Robinson acknowledged that little was known about the effect of class on performance in secondary schools, and argued that detailed value-added information was needed to help reform.

The Brunel research is set to fuel ministers’ argument that primary education must be the Government ‘s top priority.

Earlier this year studies of London boroughs found strong links between the class make-up of each area, and children’s performance in national curriculum tests.

Dr Ian McCallum, former principal research officer at the London Research Centre, found boroughs with the lowest proportion of households headed by unskilled or partly-skilled workers had the best results at key stage 2.

l Official figures for the number of young people entering the clearing system last year, which matches prospective students with surplus places, were released this week.

Around 155,000 people entered the clearing system last year, of whom 47,795 found a place.

UCAS officials have predicted an unprecedented scramble for places this year as students fight for the last free university places before tuition fees are imposed.