Gas Lockers can I

Viscount Orange Biscuit

We are planing on using the caravan more over the winter but have been told that Propane (Blue Cylinders)  gas we currently use  can freeze during cold spells and as we have the fittings for the Butane (Red Cylinders) wondered if it would be possible/legal
to set up one of the Gas changeover valve thingys (we had one in our American Caravan which when one gas cylinder finished you just turned the knob over to the full cylinder ) with propane connected to one side and Butane to the other?  any help advice gladly
accepted

All the Best

Eamonn