BS88-6 16A blade fuse.
Approx 60mm long x 14mm diameter.
A fuse is a sacrificial device which provides overcurrent protection, of either the load or source circuit. It's essential component is a metal wire or strip that melts when too much current flows, which interrupts the circuit in which it is connected. Short circuit, overloading, mismatched loads or device failure are the prime reasons for excessive current. The fuse interrupts excessive current (blows) so that further damage by overheating or fire is prevented.
When replacing a fuse, always use the correct size / type of fuse and make sure the circuit is isolated.