I too had issues with PCWorld/Currys declining my Platinum card last month. Didn't think to try any other cards but Amex confirmed they had not been asked for authorisation. I ended up ringing PCWorld and doing it over the phone which was rather odd as I gave them the number and then got an authorisation code in an email from Amex which the PCWorld chap asked for. I hesitated but gave it to him but they took ages to process the charge so that it disappeared from the pending charges screen and I had the laptop I bought before the card had been charged, although then only after a call from PCWorld to check the purchase was not fraudulent. So I suspect the problem is at Curry's end.