He is taking a cable into a CU with a spare mcb slot. All he has to do is
buy an mcb and keep that circuit separate.

It is not a good idea to have a stray socket on the wrong circuit, as it can
lead to electrocution when the wrong circuit is disabled. Subdivision of
circuits should be thought about and executed on a logical system. You don't
just put a single socket on its own MCB just because you can.

Neat and easy and not ramming too many cables into one terminal.

Have you ever installed a modern consumer unit? You could probably "ram" 10
2.5mm cables into one MCB. They are designed to swallow enourmous bundles of
cable. 3x2.5mm won't trouble it one bit.

Christian.