I can't find the thread anymore, but I remember someone wrote (very matter-of-factly) that British men aren't affectionate... lots of people rightly commented to correct them, but it stayed with me because I used to believe this too!
After ten years in the UK, four of which I've spent with my VERY affectionate OH, it sounds ridiculous now. However, it's definitely a common stereotype where I'm from - I've even had friends/family comment that my OH is "not a typical Englishman." While he's unique in many ways, I think their reaction says more about the (wrong) stereotype than his (normal level of) Englishness.
This got me thinking... if you're not British, what has positively surprised you about the UK?