I'm glad to hear that your son is being impressively calm about it all. Our children are an example to us on occasions, aren't they?
My advice, as an Appeal veteran in Bucks, would be to appeal for both, provided you can take a leaf out of your son's book and remain calm with the pressure that it will create. You have nothing to lose but your sanity!
Get the support of your son's Head, marshal every piece of academic evidence you can find and put together your best case.