Can someone identify this tune?

Can anyone identify this tune:

http://picosong.com/CR7Z/

The really recognizable part (to my ears, at least) starts at about 15 seconds.

I am 99% that it's a rearrangement of some classical piece, and I've definitely heard it before, but I have no idea what the original is called (I'm also fairly sure a short version of it is used as the opening theme to a British TV drama of some sort from 10 or 20 years ago, but that's not so important right now).