“I thought if I hadn’t got a stripy blazer and a glass of Pimms in my hand, I wouldn’t be welcome.” Although Cambridge University now admits half its UK students from state schools and colleges, the Brideshead image still lingers. It puts off many bright sixth-formers (and their teachers), convinced that Cambridge is peopled by toffee-nosed public schoolboys who wouldn’t give them the time of day.

This week, the university has been holding a conference for 500 teachers - suitably enough, half from state and half from independent schools - to dispel some of the myths and give up-to-date information on admissions procedures at one of Britain’s oldest and most prestigious universities.

Difficulties range from the need to get the special Cambridge application form off by October 15, the same date as the Universities and Colleges Admissions Service deadline, to the fact that Cambridge admissions are handled by 28 separate colleges.

It is possible to make an open application to the university (700 candidates did so this year). Applicants on this scheme are allocated by computer to the colleges with the fewest applications in their subject.

The university has been doing what it can to encourage more applicants from diverse backgrounds. The biggest single change was the abolition of the special entrance exam in 1987, always considered to favour independent school candidates, and the increasing reliance on A-levels. Since then, the total number of applications has risen from 8,400 to 10,400, with the number of applicants from the maintained sector rising steadily while the number from independent schools has fallen slightly.

But why should a sector that accounts for 10 per cent of secondary pupils still manage to account for half the places at Cambridge? Much of the answer lies in A-levels. Most applicants to Cambridge go on to get straight A grades - indeed, half the rejected applicants get three As - and 30 per cent of the applicants to higher education who get at least an Aand two Bs are in independent schools.

Which still leaves quite a bit of ground to cover before the admission system reflects the proportions of top quality candidates in the two sectors but not as much as might at first appear.

It is the students themselves who are doing most to spread the gospel that Cambridge is for bright pupils from every background. Under a programme called Target Schools, run by the Cambridge students’ union, students from Cambridge visit schools in their home area in March to talk to sixth-formers and show a video about life at Cambridge. This year, 830 students have volunteered to take part.

Alex King, a second-year student of social and political sciences at Fitzwilliam College and one of two student union officers running the scheme, says this can be extremely effective at breaking down barriers.

“They say, ‘Hey, there’s a student from Cambridge and they wear jeans too.’” Target Schools is one of several schemes trying to attract a wider variety of applicants. Another is the Group to Encourage Ethnic Minority Applications, under which students and admissions tutors visit schools and pupils visit the university.

Nine colleges also take part in the Special Entry Scheme, which makes lower offers to applicants with potential who have suffered social and educational disadvantage. This year, 16 out of 43 candidates under this scheme are holding conditional offers.

The university does not want a great increase in applications. “We couldn’t deal with them personally,” says Susan Stobbs, fellow of Pembroke and chairman of the Cambridge Admissions Forum, which consists of the college admissions tutors. “Three good applicants per place is about right. What we have to shift is the balance of sectors applying.”

Faced with a dazzling array of talent, how do the Cambridge colleges choose? Interviews, in a word. Ninety-three per cent of those who apply are interviewed and the interviews - especially those with subject specialists - are far from a gentle chat. Candidates have to show they can think on the spot and argue a case.

It is here that the university sometimes falls down on its good intentions, when some thoughtless and other-worldly college dons fail to realise how their behaviour will seem to nervous candidates.

Jane de Swiet, headteacher of the Henrietta Barnett School, a selective girls’ state school in North London with a large share of ethnic minority pupils, complained recently in The Times about the way some of her pupils had been treated at Cambridge interviews. A Muslim girl wearing a headscarf, for instance, was asked where she came from and what her parents (shopkeepers) did for a living.

But the colleges are taking action on this. Many have now issued guidelines to interviewers and the Cambridge Admissions Forum is drawing up guidelines on ethnic minority interviewing which will be vetted by the Commission for Racial Equality.

Colleges make conditional offers in most subjects based on A-levels alone; nine out of 10 students are now admitted by this route. The exceptions to this are science in some colleges and mathematics in most, where colleges also rely on performance in Special papers or STEP, a special Cambridge exam which is taken directly after A-levels.