These little 5A LA5 / LA5A / C55 fuse links are found in fuse-boxes made by Memora / MEM, Hager, Wylex, MK and more. Most commonly they are used for lighting circuits, though may also be used for other small loads like central heating boilers or alarms. They are a bit smaller (23mm long and 6.35mm in diameter) than the 5 Amp fuses used in plug tops (but look quite similar). Often these fuses blow when a light bulb blows, so it's quite common to find them blown with no actual fault in the house wiring. Though if they keep blowing, you should have your house wiring checked by an electrician.