@Dan the issue of someone replacing code on the merchant site is exactly what Barclaycard are referring to in the document they sent to me as evidence of how such integrations could be compromised. I agree it is nonsense. However I also think that all these things should be treated equally in the eyes of any legislation.

Regarding put up and shut up, I haven’t found any service able to do proper multi-currency transfers into our UK-hosted currency accounts other than to stick with the PSP/acquiring bank route. That was the sticking point with moving to Stripe in the first place, they would have to convert USD > GBP before transfer. If you know or work for such a service then I am all ears!