Thanks Mikkel.
I'd been wanting to build one for a while and now that i have, it's kept me amused for hours. Dare I say it, but it's the best layout that i have built that has felt "right"!
The loft insulation foam is great stuff. It comes in a pinky orange colour. Really light in weight and indeed very easy to cut. I used a saw to cut it to the required width - i kept the length as it was. I have heard a comment that you should wear a mask as the dust it gives off is a bit nasty. I did the cutting outside anyway and used common sense! As for mess, it was just like cutting wood really and not bad at all. Certainly nowhere near as bad as polystyrene!!
The surface of it did need a light sanding in places to get it smooth but on areas covered with ground cover/ballast etc that wouldn't really matter. I laid track directly onto it and used pva to hold the track in place and then ballasted in the usual way with no problem at all.
Cheers
Roger