Oooh! Welcome back Heron! I don't know what this is. It looks like it might be a euphorbia...but I really don't know. I hope he continues to grow it though, so we can see what it turns out to be! It looks very interesting. :)

Euphorbia lathyris and a dreadful seed weed too.

Oh...I was on the right track then...but perhaps not a good idea to let it grow on?

Thank you so much Cottagekaren , good to be back , yes you were certainly on the right track ! Thank you also Owdboggy , I looked it up and sure enough that's definitely the one ... not a very attractive plant but ime sure it has its place - somewhere ? having relayed the information to my Brother he is not keen on keeping it as part of his garden ! so great compost in the sky it will go , I said I knew someone would come up trumps - so well done , he was very impressed , querie solved ! Happy gardening both ,
Lucy .

You're welcome Lucy!

Hi, I would like you to inform your brother, that the sap of all Euphorbia plants are a skin irritant, and especially if you get it near the eyes, Derek.