In my school/sixth form the uniform policy states that girls are not allowed to wear trousers and boys are not allowed to wear skirts. Despite multiple attempts to come to a civil solution to this situation we, the student council, have failed to get this amended so that it does not discriminate. Surely in this day and age such discrimination cannot be legal in the UK? Do we have any legal grounds under which we can formally challenge the school about this blatantly sexist policy?
The answer is a clear maybe.
Discriminating on the basis of sex is illegal, however, applying different rules on uniforms is probably not discrimination under the law.
To be discriminatory it must put the class of person at an unfair disadvantage, be harassment or victimisation. You would have to demonstrate that refusing to allow females to wear trousers puts them at an unfair disadvantage (and vice versa because these are separate discriminations) - victimisation is not an issue here, harassment might be but it would have to be actually happening. You should look at things like comfort, practicality, sports, play etc.; the problem is that the better your argument for girls the worse it is for boys.😓
The steps you can take are spelled out in the link, starting with communicating with the organisation. So marshal your arguments and write them a letter and then move on to mediation.
At the very least you should get an insight into why they oppose your position. If you deal constructively with their concerns you may get what you want.