From what I can tell Parisians are not really rude. At least I didn’t meet any rude Parisians.
The Brits on the other hand - well it is a class issue. If they identify you as being of a lower class, they will be rude. My wife lived and worked in the UK and had more experience with this, but I saw it, too, in various ways.
Where and when did you live in the UK?.
What did you like and dislike (and be very honest plz)?.