Fill the bath and every spare container at the first flicker, before mains water can fail too.
Shut the fridge and keep it shut. It stays safe for about 4 hours.
Shut the freezer and keep it shut. It holds 24 to 48 hours unopened.
Move into one room you can keep warm.
Put the CO alarm somewhere you will hear it.
Then
Rotate freezer food into meals first, before anything else turns.
As the 24 to 48 hour window runs out, cook and eat the meat rather than let it spoil. If you own a pressure canner, this is what it is for, though few UK households have one and there is no British equivalent of the American process times, so follow its instructions exactly. Otherwise, dehydrating, fermenting and salt-curing (B3) are the other ways to save it.
Everything above is from the household playbook. What follows expands on it.
The card gets the first five minutes right. These are the four things it has no room for.
Ring 105 before anything else
105 is free, it works from any phone, and it connects you to your local electricity network operator. Not your supplier, who does not fix wires. The network operator, who does.
Do it even if you assume they know. For a single street, a single substation or a broken service cable to one house, they may not, and the fault is not logged until somebody reports it.
It also tells you what you actually need to know: whether it is your house or the area, whether they know about it, and what the estimated restoration time is. That single answer decides whether this is a candle-and-a-book evening or the start of the plan.
If it is only your house, check your own consumer unit first: a tripped breaker or a failed RCD looks exactly like a power cut from the inside.
The freezer rules
The card gives the windows. These are the rules that decide whether the contents survive them.
Refreezing, which is where people get it wrong in both directions:
Still hard, or still with ice crystals and cold to the touch: safe to refreeze.
Thawed but still cold: cook it, then freeze the cooked food. Do not refreeze it raw.
Thawed and warm, or thawed for hours in a warm room: do not refreeze and do not cook it back to safe. Bin it.
Anything above the surface of the water in a flooded appliance, or with any odd smell, goes regardless.
The freezer is also a cold store. In a British winter, an unheated garage, a north-facing doorstep or a box outside is colder than the fridge, and it costs nothing.
What to unplug now
Power comes back with a jolt. When a network reconnects, a great many loads come on at once, and the first minutes can be unstable.
Unplug the computer, the television and anything with a delicate power supply.
Turn off the cooker, hob and oven if any switch was on when it went. A hob left on and forgotten is how a house fire starts on restoration.
Turn off the immersion heater if it was on.
Leave one light switched on, so you know the moment it returns without staying awake for it.
Leave the fridge and freezer plugged in. They should restart, and they need to.
Then, when it returns, wait a few minutes before plugging things back in, and check the freezer contents against the rules above before assuming everything is fine.
The people to check on
This is the part of a blackout that actually causes harm in Britain, and it is not about food.
Anybody older, alone or unwell on your street. Knock. Cold indoor temperatures acting on existing conditions are the leading cause of harm in a winter outage.
Anybody with powered medical equipment. Oxygen concentrator, dialysis, CPAP, powered feed pump, stairlift, powered wheelchair. This is the group for whom a power cut is an emergency rather than an inconvenience, and it is why the Priority Services Register exists.
Anybody dependent on an electric door, lift or care alarm. A care alarm on a broadband line will not work either, per the comms companion.
Anyone with a fridge full of insulin. It is fine in a closed fridge for the four hour window, and after that it needs a plan.
Water may go too, eventually. Much of the mains network is pumped, so a widespread and prolonged outage can affect pressure. That is why the card's first instruction is to fill the bath at the first flicker rather than after thinking about it.
What this is based on
105 is the free national number connecting callers in England, Scotland and Wales to their local electricity network operator to report and check on a power cut
A closed fridge keeps food safe for around four hours, and a freezer for around 48 hours when full or around 24 hours when half full
Food that has thawed but remained cold can be cooked and then refrozen, whereas raw food that has fully thawed and warmed should not be refrozen
A full freezer holds temperature longer than a partly empty one because of the greater thermal mass
Restoration of supply can produce a surge as many loads reconnect simultaneously, and sensitive equipment is better unplugged until supply is stable
Mains water supply in many areas depends on electrically powered pumping, so a prolonged or widespread power failure can affect water pressure