Currently the Scottish Prison Service (SPS) uses a system of individual risk assessments which aims to keep anyone who poses a danger to women out of the female estate.
However, it does allow for circumstances where trans women – born biologically male – could be housed alongside women if they are deemed not to pose an unacceptable risk to them.
The Supreme Court ruling emphasised that all prisoners retain rights under the European Convention on Human Rights (ECHR), including transgender prisoners.
It accepted that Article 8, which protects private and family life, is engaged in decisions about prison accommodation.
However, the court said Article 8 does not mean there is automatically a right for a transgender prisoner to be housed in a prison designated for the opposite biological sex.
Lady Ross said the right was qualified and may be restricted where there is a legitimate justification, including maintaining sex-based segregation within the prison estate.
The judge acknowledged that exceptional circumstances could arise.
In a case involving a serious threat to life, such as a risk of suicide, Article 2 of the ECHR — which protects the right to life — might require consideration of whether accommodation in a prison for the opposite biological sex was necessary.
