Just finished changing a consumer unit for somebody. It was a fairly standard job - 2 lights, 2 rings, cooker and immersion circuits. Whilst testing the R1+R2s, discovered that the upstairs ring had one leg in a
30A BS3036 fuse, and the other in the 15A fuse labelled as immersion. The immersion itself was connected as the other leg in the 30A fuse.
The board was the original one for the house, which was built approximately 15 years ago. All good fun!