john wrote:

Run some 10mm twin and earth inside house and 10mm 3 core armour. Protect
the lot with a 40 amp mcb inside main consumer unit.

With respect, this does seem to be glossing over a number of potentially
important points.

The OP s requirements sound like they are unlikely to exceed 3kW, so
even if we allow 4kW for expansion, a 20A supply would be more than
adequate. From a voltage drop point of view 2.5mm^2 cable would just
about be in spec at 25m for that load.

You also need to decide where you will site the RCD. In this
circumstance at the head end of the supply would probably be acceptable.
Depending on the earthing system in user you may or may not have a choice.

--
Cheers,

John.

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