Woody Nightshade, by the look of it, pull it out before the berries form, which are the most poisonous part.

Yes I agree though if there are no kids around, (it's our only truly native Solanum) I would just leave it. Quite attractive in fruit I think and the birds eat them with impunity.

I have part of one that grows over into my garden from woodland. I will probably cut it back this year, as it is taking up too much room but I don't have kids and have left it up to now as the bees love it and I saw a blackcap eating the berries in winter - I had never seen one of these birds in my life before this.

It is also called 'Bitter Sweet'. I believe it belongs to the potato family. The berries are at their most poisonous when they are still green, less so when ripe.