Reviving this thread, as I just was prevented to downgrade by Amex BA Premium Plus.

The Amex agent asked for the reasons for my downgrade request, being these the new card fee of £250 plus the lesser options to use my pending 3 companion vouchers due to less travel. My maths showed that I am better off with the Classic Amex BA card.

The agent stated that I would keep my pending companion vouchers when downgrading but that I could not benefit from the welcome bonus for the Classic Amex BA. Fine by me. But then the agent said that she could not offer me the downgrade and that I had to apply for the Classic Amex BA on my own terms. If getting that card and close then the Premium Plus, I would lose my 3 companion vouchers though.

She did not provide any reason for my question of why the downgrade was not possible. I doubt that it is related to my credit score as mine has been really solid over the years and also Amex is often increasing my card limits. Forcing a customer to stick to a paid product when there is a chance to downgrade does not seem a great practice and I raise a complaint through the agent.

Am I missing something here? Has anyone been declined a downgrade before? Judging by the previous posts in this thread, it seems to be a pretty straightforward process.