Thanks to MSE for this tip. The good folks at Simplify Digital are currently offering £55 cashback if you take up a Sky HD package. Whilst this sounds less than some other cashback deals, it is the only one where you still qualify for the Sky direct offer of 12 months free Line Rental.
So you pay £49 for your box and installation, then you get £55 cashback (£6 profit). You then can choose the minimum HD subscription at £26.25 / month, and this includes your line rental. As line rental costs the same as the HD upgrade and the box is covered by the cashback, you are essentially getting HD for free.
At time of ordering for an extra £5 a month you can add Sky's decent 8MB broadband. Alternatively if you call Sky after ordering you will get 2MB broadband for free, or for £10 a month you can get a true unlimited service. You also get a free WiFi router and McAffee Internet protection Suite (better than Norton) as standard with the Broadband. Finally you also get free evening and weekend calls to landlines as standard.
Great package all in all, if you currently pay around £15 for broadband and £10 for BT line rental it is like getting Sky for free. If you currently pay for standard Sky, then sign up in the wife's name and upgrade to HD for free.