>>211682669
Britain's interests in preventing German expansion were chiefly material. Ideology didn't matter. They were both constitutional monarchies during WW1 and still fought each other.
A fascist Britain doesn't suddenly lose the former Britain's material interests because these interests stem from geography and the economy.
This alt history requires Britain to accept some kind of lesser status compared to Germany, at least within the realm of European affairs, and there's no reason to think they would, especially when fascism largely succeeds off the back of aesthetics of national strength and glory.