I have been credit crunched!

Actually that would almost certainly be an unfair term, even if something similar was in there you could (quite convincingly) argue it was unfair. It's the Unfair Terms in Consumer Contracts Regulations 1994, act, plain English explanation.

With credit card agreements you can reject some changes to your terms and conditions - basically it is a contract, so you don't have to enter into it unless you want to. This could be hit and miss as it has mostly been used to reject interest rate rises, but worth a go. See here, Step 4 'Has it behaved unfairly?'.

"We may change the terms of, or add new terms to, the Cardmember Agreement at any time, subject to applicable law. We may apply any changed or new terms to any existing and future balances on your Account, subject to applicable law."

taken direct from from Amex T&Cs on their site.