It is perfectly normal for people in the UK to have social lives if they don't drink at all, or not much or not often. I'm sorry you haven't found a social group whose company you enjoy. Yet. Blaming the whole country being a "drinking culture" is sloppy and lazy at best. Maybe find a social group based on a common interest that isn't alcohol. Maybe organise a social outing with the same people who enjoy the pub, but centred on an activity doing something different. Maybe lots of things. But definitely we shouldn't blame the inhabitants and their culture of a country we are visiting for our lack of optimal social success.

I've made very cruel fun of some British people in Hong Kong sprouting similar nonsense in defence of having no friends outside the expat community. They were actually better people than that and deserved to feel ashamed about it and to their credit they did. People from ones own culture will always be an easier social fit when overseas, even if you wouldn't have much in common with them at home. Overseas you have home and the fact you're finding out about the foreign culture in common - but it's pretty superficial and lazy to fall back on that as a basis for your friends exclusively. Moreover you will miss rather a lot of the benefits of being overseas in a foreign culture.

My experience of Brits is that they are not all such hopeless alcoholics so as to be utterly incapable of socialising without excessive alcohol. If your experience is different maybe you should ask yourself why that is. Maybe you're expecting someone else to do all the work of socialising for you as one suggestion? You may come up with others.