The performance indicators will use data on the home postcodes of students similar to those introduced by the Universities and Colleges Admissions Service this week as a tool to help institutions attract more students from under-represented groups.

The use of postcodes in the league tables - due in December - comes amid claims that providers are under pressure to favour poorer students over middle-class ones in response to the Government’s drive to widen participation. Critics say that could dilute standards.

However, education minister Baronness Blackstone was anxious to quieten such fears as she launched UCAS’s new hi-tech system. She said: “Neither UCAS nor the Government wants universities and colleges to lower their standards. Only students who have the ability, talent and potential to benefit should be admitted.”

Using a version of a commercial database developed to help companies target markets for their products, universities and colleges will be able to use postcodes to draw up a picture of the social backgrounds of their applicants. The database uses census and other information to allocate social categories to postcodes.

That will allow institutions to see which groups are under-represented both socially and geographically. They will also be able to compare data with groups of their competitors.

Tony Higgins, chief executive of UCAS, said that under-represented groups would be targeted as well as traditional students. The Government wanted to increase participation from 33 per cent to 50 per cent: “That 17 per cent has got to come from somewhere,” he said.

Despite a 20 per cent increase in students from lower socio-economic groups between 1994 and 1998, they still make up less than half the intake - and suffered a steeper fall in numbers than middle-class students in 1998 when applications fell. But Alan Smithers, professor of education at Liverpool University, said the new league tables - allied to incentive payments from the Government - would add to the pressure to select by social class rather than ability. Yet claims of under-representation were based on myth, he said.

“Lower socio-economic groups are not under-represented at university compared to A-level performance.

“The gap opens up in the earliest years. The numeracy and literacy strategies in primary schools mean we’re intervening at a much more appropriate time, but there’s no point intervening post-18,” he said.