I was over there today and I'm pretty sure that the really cheap stuff (the £2.99 hardbacks) is actually the Cold Tonnage stock which was mostly second-hand and remainder in the first place. The regular M1 stock still seems to be selling at 10% off (or 20% if you spend more than £50) which isn't as good as it sounds if you're talking about US imports given M1's tendency to convert prices at pretty much $1 = £1...
---Mark