Do international students not socialise much with british ones at uni?

I totally agree with your explanations about the culture shock there. I am from South East Asia, currenty studyin in a college in England. Although I am currently not studying in a British school, rather in an international college in England to prepare for going to a UK university. I found it hard to really get along with other students here. Not that I don't have any friends here. At first it was all really exciting to have new friends from different countries and cultures. I chat and hang out with them most of the time. But the difference in first language really limit the friendship relation, because you can't really express yourself as good as if you're using your first language. As time pass (it's my 3rd month here), I just find it exhausting to have to keep having this language barrier. And the worst part is, I only have one friend with the same nationality here.

So, I think it's totally normal for international students to tend to look for other international students from the same region/country.

After I finish college, I am going to enter a UK university next year. I am not a sociable, extrovert kind of person, but I just hope I could get along with British students and the other international students as well.

You will be fine! Naturally, everyone will feel culture shock around month 3-6. But I noticed that after 6 months suddenly everything became much easier.

The important thing is how you cope with culture shock. Some people will isolate themselves. Then it becomes much more difficult because you stop seeing your friends. No matter how frustrated you become, don't let the language barrier stop you from being sociable. Persevere, you will thank yourself later!