This is from page 7, from the below document.
There are two grades of LP gas stored at service stations. One is for automotive use only and could be a Propane/Butane mix, which is dispensed through a driveway pump into the vehicle fuel container.
The other is Propane, which is decanted into portable cylinders for barbeques and caravans.
These grades are not interchangeable and a dangerous situation could develop if the auto gas is used for domestic or leisure appliances.
Products of incomplete combustion such as carbon monoxide may cause serious or even fatal injuries.
http://npstag.com/wp-content/upload...ravans-mobile-homes-and-mobile-workplaces.pdf
This post isn't all about the legality, its more so the it my affect your build, if you aren't aware of it.
I think its stupid that there is two mixes out there for Autogas and LPG, it's so much cheaper to use Autogas than buying 9kg swap bottles