Does anyone know what plant this is?

It could be Heuchera, Sidalcea, Malva sylvestris or a young Bramble. I'd keep it for a while until it's a bit more mature.

Mmmmm..this looks familiar......perhaps its a Geum? best wait till it flowers.....

I'd bounce between Heuchera and Geum.
It's very, very similar to my geum though.

Hello Cassandra,
This could be a geum-weed as our garden is plagued by them. Unfortunately 2 summers ago I saw one or two pop up and thought whoopee that must be that "Mrs Bradshaw" (desirable geum) that I'd bought the year b4 and forgotten where I'd planted it... Well I think Mrs Bradshaw has long since snuffed it, and these dratted things, which have boring small flowers and are a pesky nuisance to pull out properly, seized their chance and seeded themselves freely about.
I do hope 4 yr sake it's something more interesting!

I would say it is Geum rivale (the one which is usually a weed), The 'flower' is not bad, but not worth keeping because it seeds so much.

I know the weed you mean Weeding, but don't know what it's called - I think the leaf is almost the same, but slightly darker green and it has long white thin roots - impossible to get rid of, pain in the proverbial, and easily mistaken for Geum

It looks like it will flower soon so I suppose you will have a clearer idea whether I should keep it or get rid, any way thanks for all your responses.