Ah, so you've had some bad experiences. Can't say I ever have. There was once the time that an insurer double charged me but I just called my bank (Barclays) and they refunded the money by next working day. I have heard that some banks can be a pain when it comes to the DD guarantee but my single experience of Barclays suggested that it worked really well.
Hmmm. I - almost - complement Barclays and BT in one post. That's a bit disturbing :)