That's an american species. I'm not aware of it being in the UK.

But I think we've established that it's one of the violets that you've got. It seeds prolifically, but you should be able to get on top of it, even among your alpines, if you pull out all the seedlings while they're still young (before flowering) and then carry on pulling it out wherever you see it.

I use it as an edging to my beds and manage not to be overwhelmed by it. It doesn't regenerate from bits of root (like couch or ground elder for example) so it's not as difficult as those to keep in check.