It's Geranium lucidum - Shining Cranesbill. It's a huge pest in my garden, my advice would be to get rid of it in the council waste bin as soon as possible or it'll be everywhere!

Edited to add that it's a British native wild flower.

Thank you Landgirl.:)..I can already see that it has a rampaging habit...but to be honest, so does Bill Wallace and I put up with that. I think I might even add this one to my garden...in the wildflower strip!

yes I have it too, it has an unpleasant smell to my mind but it is easy to pull out.

Interesting...I have yet to get up close to it! I'll keep my nose keen when I do!

It is pretty and I have them coming up everywhere, a bit the the other wild geranium, Herb Robert (G. robertianum) which is also pretty with ferny leaves.
I have both because I quite like them and so they seed!

I love them too but I do try to keep them under control, never succeeding though. They'll be with me forever. Wish things like celandine were as amenable as this little flower, now those I hate in my garden but love to see in the wild.

Creeping buttercup...that's my worst enemy in the borders...and Cleavers...how I hate those cleavers!