Flat cardboard box (with 'lid'), perhaps for carrying or storing flat items (art portfolio/canvas/posters, etc). Pretty sturdy - used to deliver a 4mm thick kitchen spash-back panel measuring 80 x 60cm. So those are the internal dimensions, and externally it's just a cm or so larger on each side. Any use to anyone before it gets recycled?
Collection from Cobham, Surrey, KT11 2AF – please say when you can collect in your reply.