Please can anyone tell me what plant this is?
That looks like one of the euphorbias ... most likely Euphorbia lathyris
Be careful not to get the milky sap on your skin as it can cause burns on a sunny day.
Caper spurge, euphorbia lathyris, seeds itself about with careless abandon. Beware the sap, mildly toxic and very painful if you get some on your fingers and then rub your eyes! Interesting in summer when the seed capsules explode with a loud 'click' releasing the seeds in a shower
Thanks everyone - didnt like the sound of it so I've pulled it up, wearing long sleeves obviously ?
We used to stop Dad weeding them out so we could watch the seed capsules exploding in the sun.