Nowhere is that made more explicit than in new rules to stop schools using under-the-table tactics to admit middle-class pupils.

From next month, schools will be required to limit the expense of school uniforms so that pricey coats and blazers are not used to deter families on low incomes. In 2003, the average secondary school uniform cost pound;185, while the average primary uniform cost pound;178, the Norwich Union insurance company found.

The new school admissions code states that governing bodies should ensure the uniform is widely available in high street shops and online, rather than from expensive sole suppliers.

The same rules apply to sports kit and other specialist equipment, with subsidies available discreetly for families on low incomes.

The code states that schools “must make it clear that any contribution to school funds and voluntary contributions to trips are not mandatory, and that the expectation is that low-income families will contribute a small amount, or nothing”.

Chris Waterman, executive director of Confed, which represents children’s services directors, said the code “has really got teeth”.

“This puts in place a fair system,” he said. “It’s now up to local authorities, admissions forums and individual schools to make sure the system works properly.”

The new mandatory code bans schools from interviewing parents and pupils, which can result in selection by the back door.

Alan Johnson, Education Secretary, said the new rules gave all children, regardless of background, a fair chance of attending the school of their choice.

“Most schools have fair admission arrangements,” he said. “The new school admissions code puts mandatory measures in place to ensure that this is the case at all schools, including the few that persist in using unfair or unnecessarily complex arrangements, which can disadvantage some families and reduce the life chances of thousands of children.”