As an aside, I'm still not convinced about NowTVs streaming quality compared to Netflix on my 4-5 Mbps connection, but I have found it easy to make 3 current ATVs use the iTunes NowTv subscription by 'restoring the purchase' or whatever the option is.
I know I've mentioned this before but if you have store credit this will get used first - Apple related things are rarely available discounted, but every few months iTunes gift cards are available at 15-20% off in Tesco, Argos, Boots, Sainsburys etc….I doubt there are many investments currently where you can make your credit stretch by that much.
I currently have a healthy amount of store credit built up, which means I'm getting Sky Movies for about £8 and the Entertainment package for around £5.40 due to credit being purchased when on offer.
The real benefit of signing up for Sky on AppleTV is that cancellation if you need to is via iTunes and therefore devoid of the hassles involved in cancelling the parent product!