Call 105 first
105 is the free national number that connects you to your local electricity network operator. Report the outage and ask for an estimated restoration time before you do anything else.
Check whether it's just you
Look at your trip switches and at your neighbours' lights. A single-property outage is usually a consumer unit issue rather than a network fault.
Protect food and warmth
Keep fridge and freezer doors closed — a full freezer holds temperature for around 24 hours. Close curtains and gather the household into one room to retain heat.
Ration your phone
Switch to low power mode immediately and use your power bank for one phone rather than all of them. Use a radio for updates instead of streaming news.