In general british culture is fading into the mass globalised mix of cultures.
That's not unique to the UK though, its just part of our globalised world, that all cultures are loosing their uniqueness and blending slowly into one. If you took 10 countries including the Uk and compared their cultural expression between now and the 1950s, or 1900s, you would find a slow convergence as more and more of what they do, what they wear, how they act/dress, what media they consume, their cultural traditions etc. overlap.
These days the best place to find authentic british culture is in the countryside.. with a few exceptions, the nearer you go to a city center, the nearer you go to the new globalised blended culture. But out in the small towns and countryside, places that are much slower to change and adapt, you can still see some uniquely british things.
Is it a good thing? that all of our cultures are slowly blending into one single culture? It probably is, if you value peace.. as we will have less differences to judge and fight over. But I do feel we will miss some of the colour in the world. If you go to historical British, Belgium, Chinese, Indian sights.. they are so diverse in culture. But if you go to the heart of the most modern part in all 4 countries major cities.. they are becoming indistinguishable.