Forgetting the availability question you will find Calor Gas Butane much cheaper than Camping Gaz.
Calor 4.5kg £13.00 £2.89 kg
Gaz 2.7kg £20.00 £7.40 kg
And from experience the Camping Gaz regulators can be pigs to unscrew or have I just been unlucky on many occasions. As you know gas always runs out at most inopportune times. I had a Scanmar 35 and for some reason the Gaz bottles were in the anchor locker, there proper housing. Changing Gaz bottle while underway at the bow when the regulator is stuck is no picnic. The soup ended up having to wait.