Its a weed to most people. A Euphorbia, can't remember which. Beware the milky sap as its caustic.

Euphorbia lathyrus, commonly known as caper spurge - its a weed.

It's only a weed if you don't want it. :)

I have something like this in my garden, it has a cottage garden look & has lots of pink bushy flowers on it but does self seed itself all over the place, just keep a check for then popping up, the root reminds me of a white carrot LOL
I don't now the name of mine?

Lol Rosierose, I love the way you keep banging away at it -- its an uphill struggle!

I think the plant underneath is a poppy as it has nodding flower buds.

I wonder if it's a "Centranthus rubra aka Red valerian", the stalks & leaves look like the one Owdboggy has just named mine that I put on here :o))

Ladyessex, your plant IS centranthus ruber - this plant in this question is not - its Euphorbia lathyrus

Oh! Right :o)