If you have Sky+ the cost of mirror subscriptions is £10 whereas it is £15 on NTL.
EDIT. I like the second question that you are asked if you order Sky online. "2. Has your household benefited from an Interactive Discount in the past? For example, have you already bought a Sky digital satellite?". Hmm, I thought that you only had to get a mindish, not but a satellite. How many millions do they cost?