Pride of Britain has hit its maximum of 50 members with the addition of the Royal Crescent hotel in Bath.
The five-red-AA-star, 45-bedroom Royal Crescent hotel in Bath is owned by the Topland Group and has a three-AA-rosette restaurant.
General manager, Jonathan Stapleton, said: "We are so pleased to be joining such a well-established and respected brand."
However, the Arch London is due to leave the 36-year-old Pride of Britain consortium at the end of the summer following its acquisition by StayWell Holdings last year. The group plans to relaunch it under its luxury, international Prince Akatori brand, so it will no longer be an independent.
Chief executive of Pride of Britain hotels, Peter Hancock, said: "We're thrilled and delighted of course to welcome the magnificent five-red-star Royal Crescent into the Pride of Britain collection, which helps to give us a very nice geographical spread."
The independent luxury hotel marketing consortium has a self-imposed limit of 50 "to guarantee quality and exclusivity" and membership is only granted following anonymous inspections and a majority ballot of member hotels. Hotels are then inspected regularly by mystery hotel inspectors, and are asked to leave if they do not meet requirements.
On whether the collection plans to extend its membership above 50 in light of hitting the limit for the first time, Hancock said: "We can't extend it without our members' consent because they would have to approve any changes to the rules, and as things are they seem to be broadly very content with the exclusive policy that we have, so I don't think that will change in the foreseeable future.
"So our plan is to keep the members we've got happy, to grow the brand and grow the reputation of the brand, and as members leave, for whatever reason, we'll replace them with the best we can find."