Correct, and mention in the BA letter than you are joining in Amex in any MCOL claim. I wouldn't threaten the MCOL route, unless you were determined to go that way. CEDR has a track record on insisting on a meaty rebooking option, there is a read-out of one such case elsewhere in this forum, so I'm fairly confident that if BA only offer a refund or voucher option without a rebooking option then BA will lose the case at CEDR level. I would have thought MCOL would be the same but it may be that BA's legal team will know of a previous case where BA was successful - I don't know of any such case.