Help explaining layout of Consumer Unit

[plugwash]

So it looks like I was right, there are two supplies coming into the CU, but they have been joined together at the metering location when a single rate meter was fitted.

At the very least you should remove the misleading "main switch" and "sub circuit switch" labels and add a label to warn people that the CU has multiple supplies.

 

[SUNRAY]

Personally I have a go at moving the sub isolator along one and move the left immersion MCB onto the RCD group then the whole of the heating section can be marked up as 'Spare'