If you’re not doing cad and such stuff I see no reason to buy a machine like that. You’re better off building a custom machine with “gaming” parts for game development.
I’ve put together a really good machine for both gaming and game development and didn’t go cheap at all with pcpartpicket set to only check stores in the UK: http://uk.pcpartpicker.com/p/PqnXzy
Final price is: £908.22 but could be significantly lower if you want to go cheaper. This is along the lines of what I would build if I had to build a machine with that budget.
All those parts are of course compatible, so you won’t have any compatibility issues or anything. It’ll also run all current games at highest settings with nice frame rate at 1080p.
I did choose a more powerful PSU than needed so you have room for upgrading later along the lines if you want to go SLI or something. You can save a bit on going with a 450 or 500W. Also you might not need two harddrives, but it’s always nice to have an SSD for OS and installing softwares on and a storage drive for other stuff.
That’s about £400-500 cheaper than building a similar machine with the link you provided to http://www.pcspecialist.co.uk/, don’t bother with these stores offering to build “custom” or even the pre-built machines they sell, they charge such overprices that it’s not even funny.
You can probably find someone to build it for you if you don’t dare to, but just know that if you can build a lego model, you can build a computer, it’s easy.