It's interesting that in amongst all the replies about what people love about Britain very few people have actually answered the question, which is what traditions and culture make you feel you belong in Britain.
The answer for me, sadly, is virtually nothing - and it's certainly not a chalk cliff. I was born to a British father under the British flag in a former British colony. I also had a Portuguese mother, and Portuguese citizenship from birth. I moved around a bit between current and former British colonies in Africa and Asia as a child so ended up at boarding school in England and have made a life here.
I still speak English with a fairly obvious Rhodesian accent but as long as I keep my mouth closed I can easily pass as white British and from behind my fairly convincing disguise I can rarely see past the sheer hostility - and duplicity - towards outsiders, no matter how British they actually are. I myself am viewed as foreign and unworthy when it suits locals, but as quintessentially British when that suits them instead - often in the context of people who are exactly like me except for the colour of their skin or the shape of their eyes.
A PP mentioned that Germans don't find rank incompetence funny. Neither do I. I don't find illteracy or innumeracy to be a source of pride. I am horrified at the lack of authenticity that plagues so many Brits, particularly when it comes to money, ostentatious displays of wealth, and perceptions of it.
I grew up with domestic staff, as well as ones working in my parents' businesses, and they were viewed as family. Service staff here are absolutely not: the class system here is designed to exclude people, not make them feel they belong.
The big thing though is the unstirring faith in British exceptionalism: the idea that 'British' is so innately superior that we cannot take lessons from anywhere alse in the world, and to suggest so is seen as unpatriotic, subversive, or downright stupid. That never makes any outsider feel they belong.