As CI goes to press comes news that American Express has blocked attempts by Curve to load Amex cards into its all-in-one wallet.

I cannot say I am remotely surprised. The addition of Amex would, for the first time, allow Curve customers to use their American Express card anywhere that Mastercard is accepted.

Amex is not obliged to work with any third parties or individual merchants, and it is quite understandable that Amex may not wish to partner with Curve. Now Curve says it will fight Amex’s decision and take its case to the relevant regulatory bodies. I should perhaps declare a minor interest in being an Amex – but not a Curve – cardholder.

Amex offers some of the most attractive rewards available on the market, and I view with caution anything that places their value in jeopardy. Curve is basically an app that enables cardholders to attach different bank and credit cards to a single Curve debit card. To be fair to Curve, it has raised more than $20m from a pretty impressive line up of renowned entrepreneurs and investors. Backers include Santander InnoVentures, Investec, Seedcamp, TransferWise founder Taavet Hinrikus, and Ed Wray, co-founder of Betfair; that is a stellar lineup.

I should also say, in the interests of balance, that the few people I know who do actually use Curve say its service is excellent and they are big fans. However, since its launch in 2016, it has seemed little more than a clever solution – but to a problem that really does not exist for most consumers: selecting whether to use Amex, a regular bank debit card or a Revolut card is not exactly the most taxing of decisions. As for the Curve Metal proposition, at £14.99 ($19.69) a month it does not come cheap.

As I understand it, Amex agreed to participate in a limited beta test involving a small number of customers. Amex then informed Curve that it would not be participating in a full rollout of the Curve e-wallet. Now Curve is claiming that Amex is in breach of payment regulations.

As CI goes to print, the Curve website continues to state: “Add your Amex cards to Curve – what if you could collect Amex points every time you shop?”

There is the argument that there is no such thing as bad publicity: in the past day or so, many consumers unaware of Curve will have read about it for the first time. All the same, it seems odd that Curve went public about partnering with Amex apparently without any agreement being reached to expand on the beta test.

Amex, historically, is a premium card service and will want to maintain that positioning. There is an argument that if consumers can shop anywhere and use their Amex, via Curve – irrespective of whether that retailer accepts Amex – then that changes the American Express business model. There is also the very important question of transaction data that is invaluable to Amex.

So this one will likely run and run, and might well be a nice little earner for some of our learned friends