Lulu was also well known when she appeared in it.
Celine Dion and Julio Engalses (sp?) both appeared in it (not for UK of course), but neither were well known at the time.
I doubt if you would get anyone well known to appear for UK nowadays as the voting is now so fixed that we would still come near the bottom even if we had Take That representing us with a song written by Gary Barlow.
Come to think of it, how about Geraldine McQueen (Peter Kay) representing UK, he/she has done OK with the two first singles.