Take one set of tubes...

I had real trouble with BOC, give air products a call, they were much more helpful, were perfectly happy to sort me out with just a pair of 80KG bottles. PM for the number if you want it.

Thanks for this. I'm going to soldier on with BOC for a bit. Partly because I have already invested time and effort with them, and also because they have a branch close to where I live.

BOC's charging structure sure is complicated though...