1. Stereotypes are not always grounded in reality.
2. I suspect in this case they are probably based on british tourists in Prague/Berlin/Vienna/Budapest getting wasted out of their minds rather than britons drinking at home.
As a Briton, I can confirm that there definitely is a significant portion of Britons that do tend to binge drink to the point of becoming violent. However, whilst significant, it's still a small portion - most Britons do not, and generally if you go into a pub, even late on a Friday or Saturday, it's full of drunk but friendly and good-natured people just relaxing and enjoying themselves.
I think, in my experience, what I've seen definitely seems to support the cultural argument. One point my friends have raised is that at Football (Soccer) matches, alcohol is generally banned because of how rowdy people get, whilst at Rugby matches beer is freely served and yet it remains good-natured.
Very much depends on the pub though. VDEs (Vertical Drinking Establishments) rely on giving the customer little else to do but drink. They don't have seating or tables, which reduces the relaxed drinking that a group would have around a table; and they play loud music which reduces talking time.
That environment sounds like hell to me, but they're very popular.
2. I suspect in this case they are probably based on british tourists in Prague/Berlin/Vienna/Budapest getting wasted out of their minds rather than britons drinking at home.