The BBC's John Young: " The Equal Opportunities Commission is backing legal action"

It is thought to be the first time the commission has intervened in such a case.

Jo Hale, 14, who attends Whickham Comprehensive in Gateshead, complains that the skirts she has to wear as part of her uniform are cold in winter and could stop her running in an emergency.

Her mother Claire, a professor at Leeds University, has tried to persuade the school governors for the past two years to allow girls to wear trousers, but to no avail.

Claire Hall says the uniform rules discriminate again girls

"Trousers are perfectly acceptable for women to wear at work," says Professor Hale, and she argues that if trousers are warmer and more practical for school, it is discriminatory for the school to deny girls the right to wear them.

"It is a sex discrimination issue. Although it is not illegal to have different dress codes for males and females, that dress code mustn't discriminate. So if girls are not allowed to wear trousers it means that they are not given the opportunity of staying as warm as boys in winter," said Professor Hale.

Dr Claire Hale and governor at the school Peter Maughan battle it out on the Today programme

The Equal Opportunities Commission is to ask the UK Government on Tuesday to request the school changes its mind. If the school refuses, it will be taken to court under the Sex Discrimination Act.

The school has so far maintained that it is not discriminating against girls because the rules - albeit for different items of clothing - apply equally to boys.

School governor Peter Maughan says parents were consulted about the uniform rules

"The fact that you are wearing a dress does not prevent you from having exactly the same opportunities as the boys wearing trousers," said parent governor, Peter Maughan.

The rules on uniform were established in consultation with parents and none of the other parents have complained, said Mr Maughan, who argues that the dress code is part of the school's "ethos".

The school argues that requiring girls to wear skirts rather than trousers makes them look smarter and that parents who choose to send their children to the school are aware of the regulations on uniform.

But there were also concerns that taking the dispute over uniforms to court could set a dangerous precedent.