I don't think you're gonna get much better than the laptop you've described for around £600.
I'm in the UK as well, so I'll have a bit of a look around for you
But what you've described might be the best.
EDIT: I checked the card in that laptop. It's BETTER than the one in mine.
My laptop can run Sims 3, all expansions and all stuff packs on High detail. I do have to turn down the number of high detail lots to 1 or 2, and turn off edge smoothing. After that, it looks and runs great.
So it'll be absolutely fine.