I quizzed my energy provider's Customer Services, just out of curiosity, and was informed, patiently and politely, that "it's for the maintenance of your SmartMeter."
Eh?
But it was installed ages ago and is read remotely - which is supposed to be the reason for the darn things to exist - nobody from the energy provider has been near it since the day it arrived!
What maintenance? The maintenance of shareholders dividends and their hefty champagne and caviar bills? Just saying........