Trumpy, Pauluk,

There are just six breakers in the consumer unit and the job, I'm not saying it's easy, doesn't look too bad.

I imagined some sort of enclosure with ALL the conections made inside it or even simply some sort of metal box with a door and separate junction boxes inside to tidy things up.

The cables need to be extended by 12 feet so would this cause any problems with volttage drop?

I just stabbed at the size of the cables when I said 10 mm. These were put in by an electrician some years ago when the garage was extended and there are no problems so they must be 16 or 25 mm as you say

Regards

David Lloyd