OK, so your original plan is perfectly sound if that's what you want to do: isolator switch after meter to give flexibility in modifying the installation, small CU next to it with initially just one circuit for the chargepoint, which exits the building and terminates at the chargepoint on the adjacent barn. Might put an earth electrode directly below the chargepoint, with the cable armour using the supplier's earth, or alternatively make the entire installation TT: ignore the supplier's earth and have an earth electrode somewhere near where the meter/CU are.
However, I'd be asking whether you need a supply to the barn for any other purpose (lighting? perhaps it already has it from another source), and also what you might do when you want a 2nd EV chargepoint - one EV tends to lead to another, at least if forum members here are typical.
So as a bare minimum I'd be planning a duct where you've dug up the ground so you can easily run in a second cable for a second chargepoint later (rather than just burying this cable directly so you have to dig it up again to add another); the alternative being to run a heavier cable now and have a CU at the barn end if that's appropriate (it may well not be, I'm just guessing at your circumstances).
You might hope so. However:
- Where is that green/yellow wire going from the earth terminal on the new supply?? It looks like it goes into the CU supplied from the house supply, but that is extremely unsound if so.
- There may be some concern over earthing in general if you've got appliances supplied from the old system within touching reach of the car on charge. If this is a farm or similar, I'd expect all the outbuildings to be using TT earth (ie. earth electrodes in the ground, not using an earth from the supply system), but seeing that connection makes me wonder. Certainly if I was installing the chargepoint I'd be poking my nose into the earthing arrangements of the existing system to be sure there's no problem.
