Hi Obs cop
I also recommend a peek at ebuyer.com - have been buying my PC components/systems there for years now.
I play Call Of Duty 4 and use FSX occasionally but you'd be hard-pressed to find a laptop that can run them both smoothly. You'll need loads of RAM, a quad core processor and the best on-board graphics you can afford. Not sure you'd find that for under £600 though.
Regards
TrafficPilot