The government has been warned of the risks associated with judging schools purely on their test scores.

In its report, the National Audit Office argued that some of the toughest secondary schools in Britain would be boosted into the top 20 per cent if factors such as pupil poverty were taken into consideration.

Although the authors conceded that grammar, single-sex and faith schools would still occupy the highest places in the league, only 272 of the UK's worst performing schools remained at the bottom of the table when social issues were accounted for.

The NAO also called on the government to change its measure of pupil poverty from the "imprecise" gauge of free school meals provision.

"Measuring and comparing the performance of schools are vital to the task of improving the education of our children," said auditor general Sir John Bourn.

"The Department [for Education and Skills] and Ofsted are now able to take into account the influence of external factors in order to analyse the difference that schools make to the academic achievements of their pupils.

"This provides a more robust and objective assessment of the relative performance of schools, and gives policy makers a firmer basis for targeting their efforts on those schools most in need of support."