Do the moving and shielding while the power is still on
Most winter power cuts arrive with a forecast, so treat the storm warning as your start time. A hutch standing in the wind loses heat far faster than one in shelter, so move it against a house wall, into the lee of a fence, or into a garage or outbuilding — never one where a car will be run with the door shut, because exhaust fumes kill faster than cold. If the hutch cannot move, build the shelter around it: a windbreak of boards or stored garden furniture on the windward side changes the temperature inside more than any single blanket.
Face the hutch front away from the prevailing wind and check the roof felting for lifted corners, because rain-soaked bedding undoes every other step. Cold is survivable; cold and damp together are the real danger for both species.
Insulate the box, then let the animals heat themselves
Cover the hutch with old blankets or a duvet, then a tarpaulin or waterproof cover over the top to keep the insulation dry, arranged so the front mesh keeps a gap for air to move — a sealed hutch traps damp air and condensation, which cools as surely as a draught. Insulate underneath too if the hutch stands on paving: a folded blanket beneath it cuts the cold rising from frozen ground.
Inside, your animals are the heating system. Pack the sleeping compartment deep with hay — far more than a normal night's bedding — so rabbits and guinea pigs can burrow in and share body warmth in an insulated nest of their own construction. Pairs and groups should stay together through the cold snap; huddling is the strategy, and separating outdoor companions in a frost removes their main source of heat. Extra hay in the day section gives them something to eat their way through all night, and digestion itself generates warmth.
Warmth you can add with no electricity
Heat pads designed for pets are warmed in a microwave, so warm them before the power fails if the outage is expected, and keep two in rotation so one is always ready to swap in. In an unplanned cut, a hot-water bottle filled with warm — never boiling — water, wrapped in fleece so no chewing teeth can reach it, tucked under the bedding layer, gives several hours of gentle heat. Never place a bare bottle against an animal, and remove it once it has gone cold, because a cold bottle against a sleeping pig becomes a heat sink working in reverse.
Guinea pigs are the exception to the outdoor plan. They lack the rabbit's coat and cold tolerance, so when a hard frost and a power cut arrive together, bring guinea pigs into the coolest indoor space you have — a porch, an unheated spare room, a shed with a window — in their own hutch or a temporary pen. The coolest room matters: moving them from frost to a heated lounge and back out again in two days is a temperature swing more dangerous than the cold itself.
Water and checks, on a rota, until the power returns
Bottles freeze at the spout first and can look full while delivering nothing, so switch to heavy bowls during the outage and expect to break ice and refill with cool fresh water several times a day. A floating ball in a wide bowl slows a skin of ice forming, but nothing replaces visits. Check the animals themselves at every visit: a rabbit or guinea pig who is hunched, cold-eared, uninterested in hay or slow to move needs to come indoors to warmth and a vet's advice if she does not perk up quickly once warm.
Write the visits down: who goes out at dark, who does the late check, who is up first. Running those checks as duties in KinsLe Care Teams, each one timestamped as it is done, means nobody assumes someone else has been out to the hutch — and in a freezing house with the lights off, that assumption is the gap a pet falls through.