Would love to do this at Asda/Tesco/Sainsburys with the 'weekly shop'
We had something similar with Sky. Sky+ box less than a year old was messing up recording, and they were going to charge us £70 call out fee plus repairs - erm, no, I don't think so!! Like someone has said, they really do try to rip you off and if you don't ask you don't get! Saying 'oh okay then, please transfer me through to subscriptions as I would like to cancel' usually does the trick.
(oh and also got us three months worth of absolutely free viewing after sending them a strongly worded complaint letter re a botched installation!)
Same thing goes with telephone, internet, insurance providers, etc.
Highly recommend Moneysavingexpert by the way, it's my godsend