beg your pardon, but
I beg your pardon, but (something)
I believe you are mistaken or incorrect; I beg to differ; I don't agree with you on that. I beg your pardon, but I believe you'll find that our school is actually one of the best in the state.
(I) beg your pardon, but...and Begging your pardon, but...
Please excuse me, but. (A very polite and formal way of interrupting, bringing something to someone's attention, or asking a question of a stranger.) Rachel: Beg your pardon, but I think your right front tire is a little low. Henry: Well, I guess it is. Thank you. John: Begging your pardon, ma'am, but weren't we on the same cruise ship in Alaska last July? Rachel: Couldn't have been me.