A school in East Sussex has been forced to lock its gates to angry pupils and parents protesting new uniform rules in which pupils are sent home if they are wearing a skirt instead of “gender neutral” trousers.

The uniform policy at Priory School has seen police called in and over 150 children and parents protesting and holding placards outside the school as the new term gets under way.

The school introduced the policy for all new pupils in 2017, over worries about the length of skirts and apparently in response to the concerns of a small number of transgender students.

Shortly before the school holidays, the school announced all students, regardless of whether they are new or not, must wear trousers in compliance with its gender-neutral uniform regulations.

“From September 2019, all Priory students will be required to wear our updated uniform,” it states on the school’s website.

On Twitter the school put out a message which read: “To ensure a smooth start to term we would appreciate your support in ensuring that your son and/or daughter arrives at school in the correct uniform. If students are not wearing the correct uniform they will be asked to return home and change into the correct uniform before entering the school.”

Parents have described the school’s position as “pointless and silly”.

“It is grossly unfair to have withdrawn a girl’s right to express themselves in a skirt,” said one protesting parent to the Brighton Argus.

The paper, which liveblogged the protest, also spoke to parent Sheila Cullen, 57, who said: “This school is obsessed with the length of skirts – it always has been.

“This new uniform police disproportionately affects girls as they’re the ones who have to buy the new uniform. It’s expensive and not fair.

“This uniform is sexist.”

Other parents have also noted the policy means if you have children in their final year they have to spend money on unnecessary clothes which will only be worn for a few terms.

Local MP, Maria Caulfield described the school’s behaviour as “disturbing”, and said it was “not how we should be treating the young women of Lewes”.

The BBC reported the school told parents in June the decision had “created more problems than we wished” but said standards of uniform had declined.

According to the school, staff are spending so much time telling pupils to correct their uniform to meet the new rules it is “detracting” from time spent teaching.

The Independent contacted the school, which confirmed it was open, despite having had to lock the gates, after The Sun and The Argus reported it had been closed as a result of the protest.

Sussex Police said: “Police attended Mountfield Road, Lewes on Friday morning (September 6) where a group of around 100 adults and children were protesting.