@MichelleofzeResistance
Was trying to find the court case: sorry, I can't track it down. Someone more clever than me will remember. But the decision was that unless a GRC was held changing legal sex, the comparator to check for less favourable treatment was someone of the same sex.
Finding the comparator in discrimination cases is notoriously difficult. In the absence of an actual comparable colleague or applicant, a claimant has to construct a
theoretical comparator to show that they were discriminated against on the basis of a protected characteristic.
So, your statement is true only when the claim is based on sex. The case that set the precedent here was of a male prisoner who identified as trans in the male estate (Green vs Secretary of State for Justice, 2013).
Green, convicted for murder and classed as a flight risk, identified as trans and was accommodated as a transgender prisoner but housed in the male estate. The prison had a strong policy on supporting prisoners who identify as trans, including a list of items that could be provided to a prisoner to facilitate their "gender expression". But items could be withheld if they could be used to facilitate escape or deemed unsafe.
Green claimed that not meeting the demands for a number of feminine-coded things was discrimination on the basis of gender reassignment, because prisoners in the female estate were allowed those things.
The judge ruled that someone who was both biologically and legally male could not claim discrimination on the basis of what female prisoners were allowed to do or have, but only the basis of what all other male prisoners could do or have.
So in this case, the correct comparator was a prisoner of the same sex.
In Home Office vs Saunders (2005) the correct comparator was found to be someone of the opposite sex.
This was a case involving a female prison officer working in the male estate who refused to do a rub-down search on a male prisoner.
At first, the Home Office had a rule that said rub-down searches could only be done by a prison officer of the same sex.
Then it was argued that not being able for a female officer to perform a rub-down search of a male prisoner would "inhibit a female officer's career prospects".
So in May 1992, the rule was changed to allow all officers to rub-down search prisoners regardless of sex. But then they decided that a) it wouldn't inhibit a male officer's career prospect not to rub-down search a female prisoner because b) a female prisoner could reasonably object to this on grounds of privacy and decency. So it was decided that male officers must not perform rub-down searches of a female prisoner.
But then in October 1992, a circular was sent out that said female officers must perform rub-down searches of a male prisoner. (No one knows how this changed from allowing rub-down searches by an opposite-sex officer to a requirement for female officers to rub-down search male prisoners).
Enter Officer Saunders. She really did not think this was appropriate, but her protests (submitted via official channels) were ignored. So from 1992 until 2003 she got around the rule by having sympathetic male colleagues step in whenever a rub-down search was required. Then she got a boss who decided that rules were rules. He demanded she rub-down search a prisoner in front of him. She refused and was transferred to the female estate against her wishes.
She claimed discrimination on the basis of sex. The Home Office argued the correct comparator was a male guard being asked to do a rub-down search of a male prisoner and a male guard refusing such a search on principle would also be disciplined.
The court however found that the correct comparator was a male officer being asked to rub-down search a female prisoner even though this wasn't permitted anyway. They found in her favour.