East of Martigny, the Rhône Valley enjoys an essentially Mediterranean climate in summer(with breeding populations of hoopoe, bee-eater and crag martin, for example), but actually gets very cold indeed in winter, often going for periods of several weeks without the temperature ever rising above 0°C. This is the vineyards in winter (31st Jan, this year, to be precise):
What it does have, however, which is lacking in England, is a
lot of sun, including during the winter. Being that much further south, the day-length in the cold months is also greater. This means that even when the official ambient temperature is low, there are hotspots on south-facing slopes where insects and lizards and other cold-blooded things can get out and about. Of course, there's no point in being out and about if there's no foodplant - but last year I did notice that wild pansy leaves and even some flowers were already out in February.
In my experience, QoS is a great sun-loving butterfly. Perhaps it is this, rather than the winter temperatures, that keeps it from setting up home in England.
Guy