All well and good tell him - smug bugger !.
Confidence I like, but cocky gets my back up.
That type of attitude does nothing to help, when you are stuck stranded 200 miles away from home with a dead car.
Dealers generally have a strong dislike to EV owners who try to provide them with information that THEY should be providing to the customer !.
E.G. - The inbuilt Sat Nav on the facelift model only displaying the current location of the car and not progressing along with the chosen route selected.
Many dealers not being able to get this resolved, but a member of the forum sorting the problem out for the benefit of himself and others, then sharing it on the forum, need I say anymore.
Point him to thread, if he needs to benefit from items that have been resolved on the internet.
They have the equipment and the training by all accounts ?.
Let's see how good he REALLY is by offering his expert knowledge in rectify the problem on your car then.
Or is it going to ( as I suspect ) be one of these type ?

of moments.
Clear the codes and ship it out !.
He could be proactive and speak to the MG Tech Team first of course, which are then likely to request they the dealer then upload's the data pack from the car, so they can remotely track and trace the problem and then provide a fix.
Of course this not likely to happen, because he disregards the information from the internet.
It's the "Bain of his life" remember.