uk fuse in fuse box can’t be sized properly because old uk installations used ring circuits in order to save copper during ww2 shortages, everybody else has this problem sorted out by now (initially by using aluminum wiring, or waiting for more copper). modern wiring is arranged in star-type topology with a few outlets per leg, and it can be fused properly, but the far out parts of circuit don’t transmit power at all times which is why it was looked down upon during shortages
example would be 16A circuit that has 5-10 16A outlets, has wires suitable to carry 16A and 16A fuse. it’s okay because you’re not expected to draw full power at all outlets at the same time, and most of the time much less than that. if you do and you know it in advance you’re expected to split it over more circuits, or make it bigger. uk ring circuit would have wires that carry only 8A in each direction, and fused 16A. it can fail in a way where one side disconnects, but the other side becomes overloaded. plug fuses are for protection of these shitty circuits from shortcircuit in appliance
more like papers over poor design informed by ww2 shortages