It's not just a British thing. Mango con chile is a popular Mexican snack.

Interesting. Now that I think of it, we used to eat semi-ripe mangos (which tasted both sour and sweet) with salt and sometimes chili powder, as kids. There is this variety of Indian mango called Rajapuri or Totapuri, slightly larger than the Alphonso ones. That was the one we ate in this way. Probably tastes good when ripe, too, but I remember eating the semi-ripe ones this way on holiday afternoons. Addictive.

Chili in chocolate is common, as are various spices in good chocolate. It's an interesting flavour combination - a lot of people don't actually like "pure sweet" flavours.

We have a bit of that in the US too. Not super popular though. Usually just chocolate but also some other stuff.

Atomic Fireballs :)