It's a weed, I don't know what its called, I always think of it as milkweed because it produces white sap, but I've spent years weeding these out in various gardens.

Hi, have a look at Euphorbia myrsinites, I agree a weed, Derek.

Looks like petty spurge, Euphorbia peplus, also sometimes called milkweed. The sap is toxic, like most Euphorbias.

I agree with Euphorbia peplus, a pesky weed!

When you pull it up take care not to get any of the white milky sap in our eye - easily done if you rub your face without thinking.