Drinking culture is normalised at UK universities, but that doesn't mean it is healthy. One survey by Northumbria and Durham Universities found that undergraduates at seven different universities in England found very high rates of dangerous drinking, with over 40 percent identified as "hazardous drinkers", 10 percent as "harmful drinkers" and another 10 percent as "probably alcohol dependent". Pub crawls and boozy night outs might be the done thing, but there are other ways of socialising.
Don't let people peer pressure you into drinking if you don't want to. Just be honest and tell people that you don't want to drink. If people give you grief about wanting to stay sober, ignore them. You need to surround yourself with people who respect your decisions.