here has been quite a lot of discussion on fuses and fuse boxes on here over the years. S1 style with the small fuse box in the engine bay is immune (carries over into early apparently S2 cars) - all these comments apply to the S2 fuse box behind the passenger side shin bin. To summarise there are two particular problems. First is that there is a metric size fuse available which will fit into the fuse holders - BUT it isn't quite long enough and will cause overheating - get the correct imperial size fuses which are still available. The second problem is much more serious and can cause major catastrophe. This fuse box was used in the P5 without any known incident, so it appears the problem is a production fault - perhaps the looms were assembled by a different supplier. The fuse box when used in the P6 is prone to melting / catching fire. This originates from the crimping of the wires into the terminations of the box being inadequate. These then overheat. It is possible to go through an intact box and nip them up to improve the mechanical connection, but once heating has started the box is toast as it deforms very easily and, if it gets to that stage, will burn enthusiastically at a very low temperature. Many people, myself amongst them have replaced the complete box with a modern equivalent.
Chris