I am Brazilian and lived in the UK for 5 years (back in Brazil though, although still visiting occasionally for work).
I grew up in a highly sociable environment and have kept many friends throughout the years from different times of my life. When I moved to the UK, of course, I knew noone (went for a PhD), and tried to make friends, of course. At the uni, I used to try constantly to do social things, inviting people I barely knew. Occasionally we would go to a pub or something, but it had to be scheduled with at least a week in advance (otherwise nobody could make it).
When hanging with English, French and German acquaintances, I had a hard time getting closer to most (with exceptions of course). Monosyllabic answers, no effort to start or continue a conversation, no apparent interest in any topic, etc. I had never really experienced this that often, with a lot of people who I had a genuinely nice impression, I just gave up, it was taking too much effort even to keep a conversation for a couple of hours.
I did a 1-week course in another uni to where a lot of my colleagues went as well. There is one story I always tell people here in Brazil... Most people stayed in a certain accomodation, but me and a German friend stayed in another one, 10 minutes walk from the first. From the pub, the way went through the first accomodation. So we sould say goodbye to everyone else and go back to our place, me and this German. He's a very nice guy, don't take me wrong, but I would try to engage on any conversation during this 10 minute-walk. His answers: "yes", "no", "ok". I felt very awkward and stopped talking. The second day, we went back in complete and absolute silence. I couldn't take it, so in the third day I invented any excuse and went back some time after him. This guy is very nice, I am still somewhat in touch with him professionally, but I just wouldn't invite him for a drink anymore.
When I met Italians, Portuguese, other Latin Americans, it was almost as if I had been friends with them for long. It all felt very natural. Our cultures are quite similar, and conversation flowed easily.
I tried as much as I could to expand my social circle, and in the end the closest friends I made in the UK came from outside the Uni, people I met through other means in general. I would say that I have good memories of quite a number of people from my times in the UK, but practically no Northern Europeans. With exceptions (for instance, I have a very good German friend with whom I still collaborate scientifically together and who is not the guy in the short story above), I learned that some people are really hard to get close to, and the vast majority of my friends (close friends and acquaintances) are foreigners (non UK).