well, I totally be might be wrong about expedia, I admit- I haven't looked that closely. But when I go to the expedia.com home page, it says
"It appears that you are currently located in the United Kingdom. Shoppers living in the United Kingdom who visit Expedia's U.S. site will not be able to purchase airline tickets or holidays. If you are living in the United Kingdom, please go to Expedia's UK site where you can purchase airline tickets and find content and promotions created specifically for our United Kingdom customers."
I took that to mean that you couldn't use a UK card, but they could be talking about something else!