Jennifer,
Butane (Blue bottle) is fine for summer vanning, but will not provide any gas when the temp drops to about 4 degrees C, as it stays a liquid in the bottle.
Propane (Red bottle) gives off gas down to below freezing, so will provide gas whatever the weather (UK weather that is).
There is consideration being given to the possible consequences of using Propane in hot weather, particularly in regard to vans fitted with bulkhead regulators.
The consideration is relating to the very high pressure build up that Propane produces in hot weather, and the ability of the Pigtail to withstand such pressures over prolonged periods.
This problem does not affect vans fitted withbottle mounted regs, as the output pressure is already regulated to 28mb, or 30mb.
Just to be on the safe side we use Butane in summer, and Propane in winter.
You will need the two different bottle fittings, or regulators if you dont have a bulkhead mounted regulator