Until earlier this year there was guidance by the cabinet office instructing that mask mandates must not be applied to those who are according to the government's published definitions (effectively self-declared) exempt.
I don't know what the legal status of that guidance had been, but its purpose had seemed to be to provide an official interpretation/application of the equality act 2010, which remains now in full force despite the guidance having earlier this year been officially declared "withdrawn."
As of August 2022, some business establishments may provide a public service but of their own free volition require its recipients to wear face coverings as a condition of doing business. While the cabinet office guidance was officially withdrawn, court decisions set precedents which certainly agreed with its interpretations of the equality act 2010, which continues to remain fully in force.
What is the legal status now of offering a venue or service to the public while excluding those who purport to be unable to wear face coverings?