Cheers mate, I haven't had a proper look as yet, but I'd guess it's not coming from the door, as it's right in the middle of the mat. I'll have a poke around in the footwell and behind the dash I think. Although, saying that, the door seals don't seem great - I've noticed water running off the bottom of the passenger door when you open it sometimes after heavy rain (although it doesn't appear to be getting into the car on that side).
Mine's an older mk4, but even so, it seems a bit strange on a 35k car. My old F-reg golf never leaked a drop!
Forgot to mention, it's never been modded with any ICE etc as far as I know, so all should be standard.