After taking in to account the suggestions received and spending far too long staring at a huge selection in the hardware store, I ended up going with the mouse poison. As the guy at the checkout kindly reminded me, I’d selected the option to give the intended recipient the most pain and suffering! I needn’t have worried about hunting down decaying bodies though. The poor wee beastie had cleaned out the tray and was lying in-situ, on its back, with its feet in the air. After a suitable burial (not easy finding an empty spot in our garden) the poison tray was refilled and, I’m glad to say, remains undisturbed.