Do knighted British celebrities find it offensive to be addressed by their first name?

Not if you address them with “Sir” first. And not the first time they are met or introduced to you.

You would initially say “Sir Paul McCartney”, then “Sir Paul” after that.

Depends on the person. It’s like when you have a PhD. Some don’t care if they are addressed as Doctor so and so. Frankly, my boyfriend gets embarrassed when I introduce him as Dr. BBE. Same for many people who have been knighted or dame’d. Some are asshats and insist on it… others are chill and cruise with the vibe.

^^I think for the most part most people with PhD’s don’t use Dr., with the one big exception that professors use it.

^^^ At least in my opinion, any use of Dr. should be limited to one’s professional world. If someone with a PhD wants to be called “Dr.” within academia or a professional society, that makes sense. I’m also ok with referring to a physician as “Dr.” at hospitals and medical practices. Out in society at large, though, there’s something very pretentious about insisting on special designations.

To get back to the original question, I think the designation “Sir” and then first name would be how you would address a knight in conversation – unless it were pillow talk.

What I know about ‘knighthood’ could be written on a thumbnail.

He is a professor and many of my friends and co workers are also.

Tradition states that you address them as Sir or Dame the first time.

After that one takes cues from the individual themselves.

I knew a Lord once. He asked everybody to call him “Jimmy”. He said he didn’t want to be confused with the savior.