You're quite correct - of course TCF does not mean you cannot put rates up - Cahoot / Abbey / Santander are doing nothing illegal.

TCF does mean communications should be "clear, fair and not misleading". I would suggest that Cahoots communications are anything but.

Whether treating customers cynically, if not to say unethically, falls within the FSA's principles based TCF remains to be seen.

Cahoot give no notice of interest rate hikes or changes in facility - what's really infuriating is the fact that they never reply to correspondence.  

However much you regulate, there'll always be sharks.

Iian