Looks like the common weedy geranium robertianum to me MandyM But i may be wrong, See what some of the others say too.

That was my first thought surreylad...herb robert

Thanks guy's, it does look like a geranium. It's seeded like buggery everywhere!

It is a very pretty weed though....!

Stinks too when you pull it out.

but it pulls out really easily thankfully.

Why pull it out? Pretty, and happy in shade. Used to be used in disorders of the blood. Culpeper says it is 'effectual in old ulcers in the privy parts'! Culpeper is worth a read, for those of you who haven't got a copy.

Best to keep the hoe going daily now, as some weeds have tiny flowers and go to seed very quickly.

I love the herb robert or wild geranium and only pull it out where it is smothering other plants. Such a dainty little plant and a cheery little flower.