Many devices (mostly electronics) have an "instant-on" feature that consumes small amounts of electricity even after you've turned it off. Remember how TV sets used to have to "warm up" after turning them on?
Usually, you can turn off the instant-on feature, but most people don't bother. I think the British have the right solution -- each outlet has an on/off switch.
TV’s used to have to “warm up” because they had tubes. That is no longer the case.
Being concerned about a miniscule amount of electricity that the clock on the coffee pot or an electronic device might use, etc. is ridiculous.
Those smart outlets consume power. It may be less than the appliance's standby power, but it is there.
Don't know about the Brits but there is a commercial with a Japanese family having a quiet evening meal when the son goes into a heavy metal riff on his amplified guitar in his bedroom. The father walks down the hall, opens the door and flips a switch on the faceplate of the floor outlet, restoring peace and quiet while he finishes his meal with a smile. The kid remains clueless. I love the look on dad's face.