Bullswood raises an interesting point. I've never thought about it before but would s75 of the consumer credit act cover you under misrepresentation or breach of contract? You bought 2 tickets for business class, paying the taxes and fees for 2 on your Amex card and yet BA in downgrading you breached the contract since you did not receive what you purchased?

"If the supplier misrepresents the goods or services, or breaches the agreement, the consumer may be able to pursue the creditor instead of the supplier, using s.75. S.75 provides that the creditor is jointly responsible with the supplier for any misrepresentations and/or breaches of contract relating to the goods or services supplied. There is no need to pursue the supplier first

The goods or services bought must cost more than £100 but less than £30,000.

An important benefit of s.75 is that the consumer is protected for the entire cost of an item or service, even if only part of the cost thereof is paid using a credit card"

https://www.edwincoe.com/blogs/main/...our-provision/