Scottish adults and children could be allowed to legally change their gender without any medical diagnosis or treatment and decide they are neither men nor women, under an overhaul of the law promised by Nicola Sturgeon.

The First Minister said that one of her top priorities if she wins May’s Holyrood elections will be to review Scotland’s gender recognition laws to ensure they are in line with “international best practice”.

Campaigners said this would mean allowing Scots to change the gender on their birth certificate using a simple self-declaration that they consider themselves to be of the opposite sex. Children under 16 would also be allowed to do this but would require the permission of their parents.

In addition, the law would recognise that some people have a “non-binary gender”, meaning they would legally be neither men nor a woman and could change documents such as birth and marriage certificates and passports to reflect that.