Oh. Here's a picture.

I assume that you have similar cans in the UK except the opening is narrower, like a half to two-thirds as wide as that one, like we used to have here.

The problem with these new ones is that the force applied to the split line is so oblique now that it's hard to open cleanly. Sometimes if you're not careful, the tab can slip past the top altogether and only push it in a little so that you have to push it the rest of the way in with your thumb. In all cases, it requires a lot more effort than the old tabs, either to make sure you're doing it right or to make sure that it doesn't splash everywhere, as if it does push the opening in properly, once it gets around the big curve, it's got a lot of velocity downward and smacks into the liquid, often spraying it everywhere (where everywhere is all over my hand).

Okay, so I'm obsessing about it a little, but the old ones worked so well.