Britain's best universities are slipping down university rankings because they are forced to focus on diversity and recruiting from disadvantaged backgrounds, experts say.

Top universities, including Oxford and Cambridge, have been under huge political pressure to take on minority students after the Prime Minister, David Cameron, attacked them for racial bias and not working harder to broaden their student mix.

Earlier this year Mr Cameron said universities would be forced to disclose the proportion of ethnic minority applicants that get places as he encouraged more transparency.