Claire Hale said the regulations at her 13-year-old daughter's school, Whickham Comprehensive in Gateshead, Tyne and Wear, were "sexist and impractical".

Mrs Hale, a professor of healthcare studies at Leeds University, said she was planning to write to the Equal Opportunities Commission after receiving the support of her MP, David Clelland.

She said she intended to sue the school under the Sex Discrimination Act, on the grounds that the dress code is illegal because it puts one sex at a disadvantage.

Claire Hale: "What do you say when she comes home freezing cold every day?"

Mrs Hale said: "It's about practicality. It's cold up here in winter and my daughter is coming home absolutely freezing, wearing three or four pairs of tights."

She said the cost of replacing laddered tights was significantly more than buying trousers for her two sons.

'Times have changed'

Mrs Hale said: "At one time, girls had to wear gymslips - people realise that items of clothing become less fashionable, and uniforms have to bear some resemblance to the apparel they wear in everyday life."

The legal action is expected to go ahead because the local education authority and the schools minister are unable to overrule a decision which was made by the school's governors.

Mrs Hale said she did not want to go ahead with the action and was hoping the governors would back down.

"The whole thing is so silly - it would be a complete and utter waste of public money to take something like this to court," she said.

Schools minister Charles Clarke has told Mrs Hale he was "sympathetic to the wish that girls should be able to wear trousers".

Ian Mearns, former education chairman on Gateshead Council, said he hoped the school would come to a "sensible arrangement" to avoid a court case.