Spoke to him.
He's fine using 4mm, but from the sounds of it , he's coming off a single socket that's a radial from the 16a mcb, will he ring it back to the socket ?
Is this good practice .
There would be a lot of wood boxing to remove to take it back to the board and there's potential for asbestos which I don't think he wants to touch.
It's not bad practice, but I would want some means to provide double pole isolation, of the outdoor circuit. Even better, if a way could be found, to put it on its own separate circuit.
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