It was. I've posted below on the main thread
What a saga. It turned out that my local dealer from whom I'd bought the car (Waylands, in Oxford) were spectacularly useless and wasted five months of my time and effort sending me in wrong directions. Thanks to a couple of people posting on this forum it seemed that other people had not had the difficulties I was experiencing. I asked one of them which repairer he'd used and he said Steer. I phoned Steer in Reading (doable from Oxford because there's a good rail link) and within 4 hours I'd got an estimate. Job was booked in, completed quickly (although there was a week's wait) with the car being collected from my home and delivered back. They had no problem sourcing a replacement bumper panel -- so why couldn't the dealership even get a price? It took months to find out that the body shops they'd advised me to use were going to rely on Waylands to source the parts, which they seemed incapable of doing.
There's a catch : my insurers are not on Steer's list of approved insurers, so I ended up being unable to make a claim, meaning I'd wasted two years of comprehensive insurance premiums (although I've been able to keep my No Claims Bonus) and foot the bill myself.
I will be making a formal complaint to the dealership and suggesting that they advise any new buyers to check that their insurers are on Steer's approved list, otherwise they may have trouble finding a repairer in the area who can both source the parts and accept an insurance job from them.
A month and a half ago I submitted a complaint to HQ through the MG website and never got a response.