Niel - Check on the web for suppliers of Cordura Nylon Tarps I have found it is a good visual match for the orginal cotton tarp matieral used on late HUPs. The stuff sews well and is tougher than cotton tarp that you can get now. I have several different colors that I have used tan, light brown and dark brown.
Could not find a UK supplier but here is a sample of colors.
http://www.americanhomeandhabitat.co...ors_FCP100.htm
I've found odd lot suppliers at much lower cost.