This is a Gothic-inspired ornamental metal clip designed for use on the corners of a coffin giving the coffin a more decorative finish. It also gave the appearance of being bound together with a more expensive metal such as brass, or in this case, silvered plates. This created the illusion of a decorative-hinged box, and was by no means a standard feature.
Corner clips came as an added extra and appear to have lost popularity after the 1960s. This coincides with the increasing popularity of cremation, which officially became more popular than burial in Britain in 1968. The coffin was becoming more practical so decorative additions slowly started to wane.