After saying this:
"Chest freezers are usually installed in a garage or utility room because of their size and their top opening lids, and work best for large households wanting to freeze food in bulk."
John Lewis are then pretty unambiguous about the issue:
"Note: manufacturers do not recommend you keep a freezer in the garage or any other outbuilding, as it may have to use much more energy. Most models require a minimum ambient temperature of 10°C (50°F) to operate efficiently. If the outside temperature is any lower, the freezer will struggle to keep your food chilled ? it may even start to defrost. If it does break down, the appliance may not be covered by the guarantee."
and:
"Ambient operating temperatures for refrigerated appliances make a difference to how hard the machine has to work to keep food at the right temperature. We really don?t recommend that you buy a frost-free freezer and keep it in a garage because it will use much more energy. Chest freezers are a better option for that environment because they?re double insulated.
Chris, Large Electrical Partner, John Lewis Newcastle"