That seems to be the correct settlement, and of course if BA had offered it in the first week there would have been no issue. If BA chose to mount a full defence then the outcome should be the same as you have here, unless there is some BA supporting factor here. The position of the refund versus the train fare - BA's position seems correct to me, you don't get a free ride here. There is a customer relations point to be made perhaps, but CEDR is not the route to do it, and nor is EC261 going to help. You would have needed to do a MCOL for both EC261 and the Consumer Rights Act to get anywhere on that, and there is no certainty. "Fending for yourself" is better than the alternative in many cases, and your best argument there is BA failed in its contractural responsibilities to provide the service, over and above the rebooking issue. I doubt it's worth £50. Interest on late payment, MCOL can provide that but BA is traditionally opposed to this as a matter of principle, albeit a principle BA usually loses at MCOL level. I'm not aware of CEDR doing anything here, and it wasn't that long ago by their standards. I guess we haven't got to a world of living with 10% inflation. If BA had paid this 6 months ago then that's about £100 of lost value here, there again the basis usually Bank of England Base Rate.

The one thing you could take further under the Montréal Convention is the car parking surcharge. It is indeed consequential and not covered by EC261. But both the Convention and the CRA would be territory for this, though I can't say you will definitely win that specific argument.

Personally I would accept.

In essence BA tends to view having to pay a full EC261 bill is their customer relations gesture, which did net you over a thousand pounds, and the fact that you had to drag it out of them is - to them - neither here nor there.