The water heater connection is certainly a little less than ideal (<- That's British understatement! [Linked Image] ).

It's acceptable here to use a breaker which opens the neutral simultaneously with all phases, but very rare to actually see that done in practice. Isolation switches for water heaters and similar fixed appliances are double-pole, however.

Fused neutrals were common in 1930s wiring. My grandparents house in London still had some of this in the 1970s. They also had an Ascot gas water heater over the kitchen sink, very similar to the one in Ranger's photo.