Have no experience of English, Scottish or Welsh fans, but when my city was hosting the Euro's many years ago everyone loved the Irish, and they got voted as "fans of the tournament". I went to Paris during the last Euro's and they are still super friendly and fun. They left a lot of trash around them (bottles and cans) but I guess all big crowds of fans do. I lived in the area of Paris where most Irish fans hung out (Montmartre) and as the rare fan of the opposing team in a sea of green that night, I had a great time and it was all fun and laughs, never was a hostile situation in the slightest.

A fun example from one of those days https://www.youtube.com/watch?v=Ipg4oxNw2b4 I lived around the corner from this. During those days the Irish fans managed to make every pub in close proximity sell out on their draught lagers. Basically they drank all the beer in every pub in one of the most pub-infested areas of Paris, lol