How come the British can pronounce Th while the rest of Europe can't?

Question

Where in their past did this develop and why didn't it spread? Are Runes ruled out because they were more prevalent than in just Ancient Britian?

Typo *Britain.

I mean, I know that other European languages don't have this sound, I just want to know why the British do have it.

Answer 1

Here's an interesting article on the subject:
http://web.cn.edu/kwheeler/IE_Main5_Grimm.html

Answer 2

Some sounds just did not emerge in some languages. The th sound is rare. It's interesting that Greek has it. When a sound doesn't exist in a language, it is difficult to learn to say and often avoided. That's why a lot of non-British English speakers seem to substitute a "d" or "t".

Answer 3

Probably for the same reason non-Spanish speakers don't roll their R's. If you don't learn it as a small child, it's tough to do comfortably.