Impressive specs. Unfortunately it appears to be £899 and therefore above of your "absolute limit" of £850. Or is there a £50 saving on that if you spend over £200 on laptops?
However, best idea would be to compare the specs with the available stock in Currys, PC World and Comet.
Although the beauty of buying from a supermarket is that they don't really know what they're selling, so when the laptop develops a fault or dies suddenly, they will probably just replace it without the fuss of a PC World Tech Guys investigation.
By the way, is Minecraft (etc) really so resource hungry - what I mean is do you really need an i7 processor and 8GB RAM? Or to put it simpler, are you wasting money when a £400-500 PC will fulfil the same function?