Get it out immediately if it is ragwort - it has a frilly leaf - and check there aren't any smaller versions not opened their flowers yet and so are not so noticeable, its a killer - also foxglove (very tall cottage garden type flowering plant, bell like flowers all the way up its stem, usually purple or white flowers, with soft large leafs at the base of the stem - lot of them out just now), get them out asap and deal with all poisonous plants by burning - if you leave them around something else might get them and the wilted versions are even more poisonous.