wandererpaul, you understood wrong. Very wrong, in fact.
The OFT said that £12 was the level at which they themselves would take legal action, and specifically stated that it did NOT mean that £12 was an acceptable amount, and that only a judge could decide what was or wasn't lawful.
Furthermore, the OFT is not a court of law, so there is no such thing as "court guidelines".
The law is quite clear: They (be bank, credit card company, or telephone company for that matter) can only charge you what your breach of contract costs them. If it cost them £10, then they would be entitled to charge £10. If it only costs them 50p, then that's what they should charge, otherwise it's unlawful. Simple as that.
I suggest a good reading of the FAQs and indeed the OFT's statement as a matter of urgency if you believe what you posted above.

__________________
Barclays: Won ~ NatWest: Won ~ Halifax (x2): Won ~ FNMF: Won ~ Barclaycard: Won ~ GHD: Won ~ Grattan: Won ~ GE Money: Won ~ Capital One: Won ~ Land of Leather: Won.
*
This wonderful site relies on donations to stay open.
Help them help us, whether it's £1 or £1000, it all helps.