Back in 1974 I had a very troublesome Renault 10 with disc brakes all round that had a persistent brake squeal, the car dealer I bought it from (non Renault) tried everything, he even replaced the new pads that were already in with new Renault branded ones etc. no joy. In the end I gave up pestering him as I felt sorry for him.
I let my brother in law, who was a qualified HGV fitter, look at it. It turned out that the guy who had fitted the new pads it already had in, had put the anti squeal shims in wrong and the dealers mechanic, not familiar with the set up, had just put the new ones, that came with the Renault pads, in the same way as the old ones came out. The BIL changed them round and put a bit of Coppaslip on the backs of the pads and all was well.
I think a bit of Coppaslip on the backs of the pads would cure the MG5's squeal, but I can't see modern mechanics or dealers actually doing this, even at a pad change, it's too old school for them.