Well good news I guess - I've had a letter back from the senior area vet, obviously as with all these things it's very carefully worded to avoid directly admitting any liability, but they have acknowledged that it seems as if the injury was missed, have apologised, says that he will be keeping a track of that vet's clinical cases and holding a further review soon, and has highlighted it on their open forum so they can discuss what everyone can learn from it. They have also offered to refund the full fees from that visit as a goodwill gesture.
Even better, I spoke to my insurance company asking them how I go about giving them the money back because obviously they paid out for that money as part of the claim, and after asking his manager, they said that as it was a goodwill gesture, I'm not under any obligation to do so
He said I can if I want, and they will deduct it from the amount left within my claim limit, or I can just keep it and be nearer to my claim limit for the year. Seems a bit crazy, but I have been honest and up front with them about it and they've said it's fine for me to keep it.
I'm pretty happy actually, I really was expecting to have been fobbed off long before now; the letter was clearly personalised to the points I had raised so it wasn't as if it was an off the shelf cut and paste response, and it does seem as if he has looked into it pretty carefully. If it prevents one other animal from being sent home with missed injuries then that's got to be a good thing, hasn't it.