ritchiesbabe, I've been looking on-line for the UK and I'm just not finding any gaming laptops that have a stand-alone video card for £400. But I'm not sure where to look for refurbished ones. Maybe you could find a couple and post the links here for someone to give you some advice?
I looked at Laptops Direct and I did find some gaming laptops, but they were all more than £400.
This appears to be a pretty good article on the best gaming laptops under £500 which might give you some ideas of what to look for. Best Gaming Laptops Under £500