Well I finally plucked up courage to go to the garage and fill the gas tank with LPG.The nearest garage with gas pump is only a few miles from home.
It's really very simple and instructions are in the pump. There's an 80% cut off valve, so the pump automatically stops when the valve shuts.The price was good too! And works out much cheaper than getting bottles exchanged.
Now ready to fit the hob and test everything.