Full strength battery acid wont freeze at any temperature likely to be found in the UK. However in a deeply discharged battery the acid becomes more dilute and it can freeze in severe weather. In polar regions it can be worth removing a vehicle battery and bringing it inside overnight. Alternatively many vehicles have an electric engine block heater in severe climates, some models include a small heater to warm the battery, and also a trickle charger for the battery.
Most businesses and homes have outdoor 120 volt, 15 amp outlets for engine block heaters.
