Its Mare's tail (Equisetum arvense). Very deep rooted weed so don't try to pull it out. You need to slightly crush it so as to break the coating and then apply a strong weed killer with perhaps a brush, being mindful of nearby plants. You might need to do this several times so keep at it.

Hi, it is Equisetum arvense, but rather than mare's tail, it's horse tail, mare's tail is an aquatic plant, Hippuris vulgaris, Derek.