We used some sort of drainage tube.Black plastic, about 12 inch dia, corrugated on the outside but smooth on the inside, think they came in 12ft lengths.

I have some USED ONES here in Texas but it would cost to much to ship to UK

I got some years ago from a place that makes aluminum cans the tube were cores for rolls of aluminum. I had to glue 2 together to get them long enough. Yoy might check on places that make cans in your area.

Why not build a box racking to spec of the space you have or the amount of material size you may need? Sorted in colours, manufactures etc etc

I use large quickcrete tubes (for burying in the ground and pouring concrete in) from Home Depot and they work great!

http://forum.thehogring.com/discussion/435/cardboard-tubes-for-material-storage

Had these up for sale, retail per tube was $90.00
1/2" cardboard made for a solid structure.

I did see those but im in the uk …………………. if I was in usa I can get the concrete ones from home depot for $5 each

concrete tubes when you stack over a couple high on each other crush they smash from the weight. Have these stacked 10 high with material in them and haven't even thought of collapsing.