You failed to directly answer the question regarding a legal requirement to serve a fresh pint in a fresh glass. I drink cider; there is no reason to dip the tap into the pint and I wish to retain my glass. I am a customer: can the landlord decline to serve me with my “used” glass and on what basis?
Yes! The Landlord can refuse to serve who he likes, he is in charge of the pub and it is his license.