There's a common misunderstanding that you must be born, or live in, Britain to be called “British.” This is wrong. Anyone can be British. It’s an identity you just pick up and wear at will. Like being a Goth, or black. Here is how you do it.
1. Secretly hate yourself, but even more secretly love yourself.
You must be self-deprecating at all times. Behave like Hugh Grant and constantly project an image of “fish out of water” charm. You are well-educated and know a few things about a few things, but golly, you’re a very silly person really and don’t deserve any of this attention and my goodness, you're a total fraud. In private, admit the truth: you are British. We invented everything. Then we ruined all of Africa and half of Asia, and people still think we’re classy and adorable. You’re one pimp motherfucker.
2. Believe all Germans are Nazis.
This is easy because it is true. All Germans are sneaky Nazis. Thank goodness for the British who single-handedly defeated them while the Americans watched in wonder. Be sure to remind all Germans that you think they are Nazis by constantly making jokes about the Second World War, Hitler, and how they love Hitler. If they get offended by this (i.e. accusing them of sympathy with the worst regime in human history), this is just another example of them having no sense of humor. Which is typical for a Nazi.
3. Polite = rude.
To be truly British, politeness must be a weapon. “I do beg your pardon” is British for “don't bump into me. Handle your business, you clumsy fuck.” Whenever you wish to display hatred or anger, be excessively polite. It’s been working for us for centuries. That’s why we ruin everything but people still think we’re admirable.
If you do these three things, you are well on your way to becoming British.