Britain's leading universities have overhauled their admissions procedures in an attempt to socially engineer their intake by favouring students with lower exam grades if they come from poor families.

Admissions staff have been instructed to give extra points to candidates whose parents did not go to university and to favour talented applicants if they attended poorly performing comprehensives.

The policies show attempts at positive discrimination in favour of those from deprived backgrounds as universities try to curb the domination of higher education by the best-performing state and independent schools.

The institutions that have drawn up the most systematic policies to favour pupils from poor families include Edinburgh and St Andrews. Cambridge and some departments at Bristol also use statistical models to favour pupils from less successful schools, while Liverpool and Manchester have signalled they will move in that direction.

Documents released under the Freedom of Information Act show that numerous universities try to give various advantages to candidates from poor families.

The policies are a reaction to government pressure to change the social profile of higher education. John Denham, the universities secretary, has accused leading institutions of “social bias” against the poor, leading to a “huge waste” of talent.

The institutions all deny social engineering. They insist their systems are designed to uncover candidates with the greatest academic potential regardless of social background. Critics, however, warn that universities cannot hope to cancel out the failings of secondary schools.

“It’s a minefield,” said Alison Wolf, professor of public sector management at King’s College London. “Of course there should be a mechanism for spotting those who can really make it and of course one should take into account where they went to school, but you cannot sort out a deep-seated social problem by giving kids extra points because of the schools they went to.”

At Edinburgh, ranked 14th in The Sunday Times University Guide, tutors use a complex points system to aid candidates from poorer backgrounds.

All applicants for the most popular courses are given a score based on their GCSE grades and predicted A-levels, or their Scottish equivalents. Any candidate considered disadvantaged is awarded extra points – someone who would be the first in their family to attend university, for example, gets two. There is also a sliding scale of points to compensate those who attended poorly performing schools (up to six points) and another to help those from comprehensives in the surrounding area (up to two points).

The university advises staff that a total of eight points – in addition to the basic entry requirement of three Bs at A-level – should be enough to secure an offer. It means candidates from the most deprived backgrounds can win a place there with three Bs while most others would need at least two As and a B.

“We are trying to look at students who don’t have advantages and to reflect their achievements in context,” said Elizabeth Lister, Edinburgh’s director of admissions. “If we operated a system simply of academic grades, [some] students would be extremely advantaged because they have such support and the quality of teaching and educational environment. So would that be fair?”

Cambridge operates a more limited points system, helping applicants whose schools come low down GCSE league tables. Geoff Parks, Cambridge’s admissions director, said: “Nobody gets in or out because of GCSEs; it is simply an attempt to capture what I would say is the unarguable fact that your performance at GCSE is influenced by the quality of the school you attend.”

Some departments at Bristol, including the law school, also use a points system. Oxford has a less formalised approach. It asks on application forms about the performance of a candidate’s school but has advised staff it should be used to “gain a general understanding” of the pupil.

St Andrews, which was attended by Prince William, marks application forms with code letters indicating whether the candidate is entitled to help under a series of “access” schemes. Its admissions handbook advises staff that “any requirements may be waived . . . to promote wider access”.

Other universities have a less sweeping approach. “It is never going to be an exact science but we do want to change our social profile so we are more representative of society,” said Steve Smith, vice-chancellor of Exeter University, where 27.5% of students come from the private sector, compared with more than 32% five years ago.

“We may soften our offers, perhaps from AAA to AAB . . . for someone who comes from a school that performs badly.”

Several universities, including Birmingham and Manchester, do not automatically give extra points to pupils from poor backgrounds but run rigorous courses to find the most able.

Kimberley Anderson, 19, a comprehensive pupil from Sutton Coldfield, benefited from the A2B scheme at Birmingham, in which pupils are put through a series of essays and assessments. Only if they do well are they given a head start in admissions.

“A few did go to university from my school but not many. I was worried that you needed very high grades to get in,” Anderson said. “The programme lowers the grades you need and that’s why I chose Birmingham.”

Claims of university discrimination against middle-class candidates under government pressure erupted in 2003 when independent schools discouraged pupils from applying to some courses at Bristol and elsewhere, alleging unfair policies.

Few of the new systems discriminate explicitly against independent schools, but that may change. Documents from Liverpool University state: “Students from independent schools appear to do less well than those from state schools and colleges, all other things being equal.”

The university is now considering how data on the type of school attended by a candidate should affect their application.

David Willetts, the shadow universities secretary, warned there was a “real danger of rough justice” if institutions adopted blanket policies to compensate applicants from poorer backgrounds.

“This results from universities having to pick up the consequences of very limited educational opportunities in too many parts of our country,” he said.

— Additional reporting: Tom Gordon

The student split

Leading universities and their percentage of UK students from independent schools

1 Cambridge 45%
2 Oxford 46.3%
3 LSE 40.6%
4 Imperial College London 38.7%
5 University College London 37.6%
6 St Andrews 39.1%
7 Warwick 34%
8 York 22.1%%
9 Bath 24.1%
10 Bristol 34.9%
11 Durham 32.2%
12 King’s College London 29.7%

— Universities ranked according to The Sunday Times University Guide

University admissions policies: Bath | Bristol | Cambridge | Durham | East Anglia | Edinburgh | Exeter 1 2 3 | Imperial College | King's College | Liverpool | Manchester (review) | Newcastle | St Andrews | York | Warwick 1 2

Times recommends

• ‘Obama effect’ pushes British pupils to US
• Over-subscribed colleges face budget shortfall
• End in sight for school tables based on test results