Worth citing here, I think, following from Wikipedia's article on "Linking and Intrusive R"

... recognizable examples are the Beatles singing: "I saw-r-a film today, oh boy" in the song "A Day in the Life", from their 1967 Sgt. Pepper's Lonely Hearts Club Band album, or at the Sanctus in the Catholic Mass: "Hosanna-r-in the highest". This is now common enough in parts of England that, by 1997, the linguist John C. Wells considered it objectively part of Received Pronunciation

~M~