Having traveled mostly through the North of England, i can honestly say I've never found English people to be downright unfriendly; however, there are differences. I find Liverpulians to be the absolute friendliest people on earth (with the possible exception of their cousins in Ireland). I made so many life long friends in Liverpool, I couldn't begin to count them all. They truly make me feel like one of the 'family' evertime I'm in their company.
On the other hand, I often find middle to upper-middle class Brits from the suburban stockbroker belt of London (Home Counties) to be rather standoffish and cold. Maybe it's a class thing, I don't know.
One major wall in communication between Brits and American's revolves around humour. I find British humour to be a little dry and word oriented. American humour is more built around situations and a lot more expressive. Most English people--and Southern English people in particular--aren't terribly comfortable with back-slapping, side splitting type stuff. Curiously, I find Irish people to be very much in tune with American humour and mannerisms. That must be due to the long history of immigration to America. I see Liverpudlians as being half-way to an American sense of humour as well, but again, you'll still find a lot of that droll play on words type stuff with Scousers as well.