Scores of schools, including primary and secondary, academies and private, have adopted policies allowing children to carefully choose clothes "in relation to their gender identity".

George Abbot School, an academy school in Guildford, said it "[avoids] listing uniform items based on gender" so all pupils can "wear the uniform they feel most comfortable in or that most reflects their self-identified gender".

It said its decision is bound by its legal duties under the Equality Act 2010, which prohibits discrimination based on characteristics including sex or gender reassignment.

The secondary school offers a single list of approved items for all pupils, which incudes a blazer, tie, shirt and trousers and/or skirt.

Last year Suella Braverman - at the time the government's chief legal adviser as attorney general - said schools have no legal obligation to accommodate children who want to change gender under current legislation.

Brighton College, which charges £30,000 a year for day students and £65,000 for boarders, has rejected girls' and boys' uniforms in favour of 'Uniform A' and a 'Uniform B'.

Uniform A includes a white open-neck blouse with a skirt or trousers, while Uniform B includes a shirt, tie, jacket and trousers.

The school says it wants to accommodate children wishing to "make a thoughtful and considered choice about the clothes worn at school in relation to their gender identity".

Valley Primary School in Kent says "all children have equal access to wearing school uniform regardless of their culture, race, religion, gender, disability or ability", while some are less explicit, with Beaumont Primary Academy in Huddersfield simply stating that its one list of uniform clothing is "worn by all pupils".

Retired head Chris McGovern, chairman of the Campaign for Real Education, told the Mail on Sunday: "Schools are adding to the mental health problems of children who, after going into school, no longer know what gender they belong to."

He called on the government to intervene.

But the National Education Union says it is "not good practice to make girls and boys wear different uniforms".

A gender-neutral uniform policy allows students to "present themselves in a way that makes them comfortable and confident", it says in its advice on supporting trans and gender questioning students.

Read more: List of all the schools we know are affected by concrete safety fears

Uniform is just one of many gender related issues schools are grappling with.

Many must also answer questions on its toilets, changing rooms, and which pronouns should be used.

Portsmouth Education Partnership, which works with all schools in the area, says all pupils "have the right to access the toilet that corresponds to their gender identity".

"Ideally, schools would provide single stall accessible toilets that can be used by all," it says in its Trans Inclusion Guidance.

It comes as more than a hundred schools are having to tell parents last-minute that they are not opening on time due to safety fears over a certain type of concrete.