I found what appears to be a limited supply of the "good stuff" to use for 4-season tent inner fabric. This un-dyed white rip-stop nylon seems to be 30D, pure finish, not calendared, and uncoated rip stop nylon(based on the 38gsm weight shown on their Web Site for the same thing but coated finished product also for sale on their Web Site).
Keep in mind, most of the uncoated breathable nylon typically for sale on the normal sites are down proof, calendared, and therefore are not ideal for inner tent fabrics. This pure finish stuff should be much more breathable for 4-season and other MYOG uses (think 4-season inner nets for your mid, sand-proof panels for desert shelters, etc.)
Being that the shop selling it is in the UK, it might well be some rejects that Carrington intended for parachutes that Roger speaks so highly of for his tunnels???
Regardless, at just 99 pence/meter ($1.66 or so per meter in USD), it's worth taking the chance on it. I just bought 12 meters of it and it only put me back $20.93 of her majesty's finest sterling...That's with shipping to the states too!