Fighter jet intercepts of international flights

[Overtone]

I recently flew from Delhi to LHR on a BA widebody. Flight route took us pretty close to Berlin. In between the eastern border of Germany and Berlin, while flying basically due west, a fighter came out of the north and passed us very close, slightly above our flight level and slightly behind.

Does anyone know: is this an air defense intercept that occurs routinely / frequently? I could imagine they would want to take a look in case a small jet is flying in close formation behind the widebody and hiding in its radar shadow. Is there some other reason?

If this is routine, is it something many countries do or is it particularly a habit of the old NATO frontline states?

As you can tell, I have lots of speculation; would be interested to learn more.

Thanks.

[Noah Zark.]

Any idea what type the fighter was, in that it might give us a clue as to whom it belonged, and therefore what was the purpose of the "intercept", i.e. friendly force, just passing by, practise intercept, not-so-friendly force (at the moment!) a spot of intimidation.