you'll have to save up a bit more to get anything worthwhile. £550 is about the lowest you can find the cheapest laptop with a decent GPU that won't suck.
when you do save up that much check out this: http
/www.pcspecialist.co.uk/notebooks/cosmosII/
then customise it with an I3, 8GB of ram. that's the only changes you need to make - if you don't need a copy of the OS then you can cut the cost down to around £480 ish.
anything below this won't really do a great job at gaming, even at 720p