No RCBO on Shower and Burnt out connections on Main Fuse

While working in a house fixing lights, I discovered there was no RCBO (essential safety switch) fitted to the shower circuit. When I opened up the fuse board to fit an RCBO on the shower circuit I discovered the main fuse had been overheating and the insulation on the cable had started to melt (see image).

There should be an RCBO or RCD on all electric showers. See link in next post.