Well for a start off, what level of gaming do you want? Serious high end £1200+? Or something averagely decent?
The specs in my sig are from a Lenovo APU system with dual graphics cards (works a treat on all games except those benchmark games like crysis and BF3) only cost me £499. A really good mid ground laptop. I can play a varity of games (not indie titles either!?) @ medium to high settings. I get a solid 60fps on blops2 oh medium and 45/60 on high.
Tl:dr what you looking to spend and what type of specs? Low med high end gaming?
3. Do brands really matter? (alienware, acer, toshiba etc.)
I would not bother with a gaming laptop. They are far too expensive, and for the most part you can't upgrade them the way you do a desktop PC.
If you are Scrooge McDuck, and you're swimming in gold, I guess you can drop $2000 to do what a $1000 (upgradeable) desktop can do. It's really a bad value any way you slice it.
I hate posts like this. Until the tc states a purpose, assume he has a reason for wanting a laptop. For all the value of a desktop, mine still can't be taken with me on my frequent travels. I'm assuming the same is true for most people.