Televisions, games consoles, speakers, monitors and other electrical devices have become such a normal part of British homes that it is easy to forget how many remain connected to the mains around the clock. Switching something off with its remote control or power button does not necessarily mean that it has stopped using electricity. Many devices enter standby mode instead, where they continue to draw a small amount of power while waiting to be used again. On an individual device, the cost can be tiny. Across a house with dozens of electrical products, however, those small amounts of electricity can…