WTB Foamboard

I gather Hobbycraft sell it too, best call them first though, not having had first hand experience............
http://www.hobbycraft.co.uk/

Otherwise a quick 'Google' pulls up lots of options:
http://www.google.co.uk/search?hl=en&q...board&meta=

If you intend to handle the layout alot (which is likely due to the portabilty), you may want to use a little ply (general model shops that supply boat and aeroplane modellers will have better and thinner stuff than your local DIY centre) or timber on areas that might get knocked (foamboard doesn't take imacts too well, despite being strong in other areas) or handled.

The foamboard I used used in the mag feature was from ex display boards.

The pic below shows the 3mm ply facia along the front. The curved backscene is 3mm ply too. The darker areas on the top are cork floor tiles which are just cosmetic to raise the track slightly and to allow a surface I can set the buildings into. Of course, foamboard would be just as good, just I'd run out and had the tiles to hand.

Ah, never considered hobby shops, thought it would be a DIY thing!

Many thanks for everyone's help