No wonder, it is dangling down, all the sap is rushing to the top of the plant!
No idea what it is though, sorry.

It is in a garden we inherited so no idea if it is a weed or a plant. Thanks anyway for input.

It's a bit hard to say with it being upside down but it does look like a weed to me. At least, it looks very much like one of the weeds I'm frequently pulling up in my garden!

I know it well but for the life of me can't put a name to it. I'll be kind and call it a wild flower because a weed is only a plant growing in the wrong place (a rose is a weed in a chamomile lawn if you don't want it). You may however want to get rid of this as it seeds all over the place.

Rosebay willowherb has just come to my mind.

Thank you all for your comments, I will be digging it up today.