So thinking out load now, if Im paying 40 notes for 15kg of Calor Butane, which isn't much different to 15 litres of the stuff, so about 2.60 a litre, whats to stop me from creating some clever pipeworks and fill up and use Lpg for my ocasional heating.
LPG road fuel is mostly propane, although they do mix a little butane into road LPG. Propane has a much higher vapour pressure, so if your cylinder and appliance aren't designed for it, I'll see you shortly following your re-entry. 
Pronane, even better then, the Red Calor Gas Bottles are Propane.

. and it's about 0.5kg/l, so you're getting twice as much as you think in the cylinder.
Not a big enough margin to be worth messing about.
Ok, got that wrong then, so just over half capacity, so about 1.34 per litre compared to LPG at 60p.

Similar to Petrol vs LPG prices, so surely enough margin to mess about with, bearing in mind aome people go to the trouble of getting there Cars modified for the same margins at a much higher midification cost.
