Hello, could it be ground elder, the leaves are very similar and the way they are spaced, if so it can be very invasive, leave in the pot and see if it sends up slender stalk with white flower. julien

I thought the same as Julien. It looks very much like the ground elder weed. It has managed to get into my borders. I have a right battle trying to keep it from spreading and over taking the rest of the garden.

Yep, I'd say it's ground elder too. I'm constantly having to pick it out. Whatever you do, don't plant it!

And keep an eye on the roots at the bottom of the pot, they will reach out and walk too.

You can eat Ground Elder not my first choice of salad but mixed in it is fine.

Thanks everyone for your replies, ...Binned it!!!!