I would like to but I don't feel familiar with british websites that offer gaming laptops for a good price so I suggest you to intestigate where to find cheap laptops so then
I can select one from the site.
But it's not that difficult to choose one as you have no much money, so the only thing that really matters is a decent GPU. GDDR5 if possible maybe a GTX 950M, 860M, GTX 850M or any other GPU with similar performance. If the money isn't enough grab an R7 M260, GT 940M, etc. Here you can check a laptops GPUs ranking:
http://www.notebookcheck.net/Mobile-Graphics-Cards-Benchmark-List.844.0.html
It's the only spec you should really consider due to with 300gbp no one will offer great features.
If it's possible try not to get a big...