RCD tripping when appliance switched on

[plugwash]

Thanks to everyone for your replies, sorry to be late in my response, my mistake, the sockets that was in place was "Double", one in each bedroom, the cables was entering the patress boxes protruding app. four inches from the floor boards (on surface) as the house is empty at the moment he thought it would be a good idea to replace them, unfortunately and against the "P" regs he disconnected the connections at the c/unit

Afaict this is not in itself a violation of part P

and Bernardgreen was spot on, he had replaced the neutral on to the wrong bar, they seem to be OK now,

An easy mistake to make for those not used to modern RCD arrangements.

the ground floor is also in need of re-wiring and there is no cooker point, I have arranged for a qualified electrician to view the system and quote for re-wiring,

If it were me I'd get the existing wiring checked out before jumping to the conclusion that complete rewiting is needed. Sure if it's old rubber cable then it should be replaced but PVC cable lasts practically forever under domestic conditions unless it's either faulty or abused.

I doubt that he will compromise his or his family's safety again, thanks for your advice and fair criticism

I think you are being a bit hard on your son there. He made a small mistake that did not cause any real danger.

Yes qualified electricians do a load of testing that diyers don't but for years nearly nobody did any significant testing and the vast majority of us are still here.