Like this is the ultimate gotcha.
There are also exceptions which allow service providers to discriminate on the grounds of age, pregnancy & other protected characteristics, if there is a good reason for the policy.
These policies rely on people being sensible, reading the sign and complying (and it they don't it might be pointed out to them)
When Amelia Pereira (pictured here on a 'girl day') demanded to use the ladies at the Rockhouse pub & was declined (the accessible toilet was offered) it made the papers & the pub apologised mirror.co.uk/news/uk-news/t…
(the manager shouldn't have asked about 'sex change' though)