Microsoft store has the Sunset overdrive special edition Xbox one (White) with Forza 5 for £309.99. However, Quidco has £40 cashback on Xbox One purchase at the moment so it brings the price down to £269.99.
The only thing that I'm a little unsure of is Quidco saying the bundle costs £329.99, which is incorrect.
Quidco also has 15% cashback on Forza Horizon 2, and Halo Master Chief Collection as well. Check those out too.