So in accordance to the lore of Mumsnet I have now given up margarine in favour of good honest butter.
Over the summer it was fine, I have a thermal dish and it lived in the cupboard and it worked well, keeping fresh even on the hottest day.
Over the winter I have changed to a glass butter dish and kept the butter on the side in the kitchen but even though the house is warm the butter is solid.
I have taken to doing what my great aunt (who was a dairy maid) used to do which is to pop the butter on the radiator for a few minutes before use.
My question is how to keep butter soft enough on a cold day?