I have just acquired a BT SmartHub 2 with one WiFi disc from BT just for extending my contract on a fixed price for 18 months.
After checking for best location for the disc I now have a full signal all around the house with a small drop off in my Lounge.
I should add that it is quite a large 4 bedroom house and the Lounge I built is on the end so its at the opposite end of the building and through the original outside wall.
I contacted BT and they have promised me an extra WiFi disc this week (for free) and if that was not enough they would send me an extra disc also free of charge.
I have now disconnected all my powerline range extenders and will put them on Ebay. I think that this is a win win situation.