I need to install a second CU on the opposite side of an inner (cavity)
wall to the side that has the: meter, isolator switch, Henley block and
existing CU. Once the new CU is in place I'll be transferring several
circuits to it and the old one will just be for the garage and
outbuildings. Currently the walls are bare block but will either be
plastered or dry lined later.
The question is how to protect the tails between the Henley block and
the new CU, and how to mount the CU. The distance will be about 3m.

The current plan is to sleeve the hole in the wall with waste pipe and
to either use metal trunking or wooden boxing on the walls to protect
the tails and provide access when the walls are plastered. Above the CU
I plan to provide a boxed-in area (with a removable lid) for the cable
drops.

I presume a flush-mounted CU is the way to go, but I'm open to other
suggestions. Are any particular types recommended? I'll probably have a
mix of RCBOs, MCBs and RCD ... I'd like to go all RCBO but the cost is
very high.