Home LPG – cheapest supplier in Herts??

[seadragon]

Our new house works off LPG, so have Calor bottles but they are more expensive than Flogas (47kg butane). I would change to Flogas but not sure if there are any gas suppliers who would take my Calor and exchange for Flogas. If not the next option is to find a Calor supplier, preferably close to Stevenage area that is cheaper than the rest, Calor is more expensive than Flogas and don’t see the point in paying about £15/bottle more than I need to.

Any help/advice much appreciated