Not related to Amex but still keen to share this;

When I bought my car 3 years ago, I paid for it by debit card (HSBC Advance). As I was fresh into the country I wasn't allowed to take up any CC's yet (no credit history in the UK) so couldn't try..

Anyways, the procedure with a debit card is quite strict, they phone up the bank and you need to confirm the payment in order for it to go through. All done, got the keys and my new car and drove away.

5 mins later - hm, the petrol tank is quite low, let's go to and fill it up.
Went to a local Sainsbury's filled up the tank and went to pay - *boom* sorry sir your card has been declined.

There you are with a fiver in your wallet, a brand new car and no means of paying for your fuel!!

Highly annoying. I spent about 1 hour at the petrol station whilst they were making phone calls to both their bank as well as mine in order to get my card unlocked so that they could take payment for the fuel.