Hi Dave!,
That sounds like a mission and a half, with a job like that.
Personally, I wouldn't like to see an Electrician use a heap of junction boxes to do a job like this, but at the end of the day, there are going to have to be some junctions made.
Is there a possibility of moving the Unit to suit the runs of cable, to minimise the number of joints required?.
Over here, you can pretty much put a Consumer Unit where you like as long as it's away from sources of moisture and it's easily accessible.
I've shifted switch-boards here before and believe me, it's not a job I'd like to wish on anyone!. [Linked Image]