Legal aspects and landowner responsibilities with respect to ragwort can be found on page 2 of this document: https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/69264/pb9840-cop-ragwort.pdf Essentially it is the occupier of the land that is responsible for controlling any injurious weeds growing on it though, as has been pointed out, it is only when the occupier fails to comply with a notice that an actual offence is committed. The occupier may or may not be the landowner and whoever made the original complaint may consider Gladwish Land Sales to be the occupier.