I've heard LPG is a by-product of the refining process that gives us petrol, diesel and a few other products from crude oil. Given it's a by-product, i wonder if a very small value is attached to it by the oil companies and as such most of the price is made up of Fuel Duty the same as petrol/diesel?
Just a thought, no idea if it's right though!
To a degree yes, but the duty is much lower on LPG than petrol/diesel so doesn't play as much of a part.
A lot of it will be what people are willing to pay - if their sales start dropping off the price seems to drop as well to compensate.
The price has tended to rise when weather is colder as its used for heating/cooking as well, the increased demand increases the price.
It does vary greatly though - The most expensive prices are double the cheapest on lpg, you don't get that with other road fuels.