replacing old consumer unit in garage with new

[Engineer54]

The original board has a 6 amp mcb for lighting, with 4 lives coming out of it? I'd want to know where these were going.
and the water heater fault took out a 45 amp mcb? But only when the lights where turned on?
ummmmmmm

Haha, we don't even know, because the OP has neglected to tell us, what size this SWA cable is, or if it's a 3 core or a 2 core?? All we know is that it's protected by a 45A MCB!!