What could realistically happen
The figures below come from the National Risk Register 2025, the government’s public assessment of serious risks to the UK. Each score describes a “reasonable worst-case”, not the everyday version of the same event, which is usually milder and more common.
Likelihood is the chance of that worst-case happening at least once in the five-year assessment period used for non-malicious risks (weather, accidents and system failures). None of this is a forecast for your street. It is a way to think clearly about why a short reserve of water, food and light is a sensible household habit.
Power cuts
Regional worst-case: moderate impact, 1–5%
Local cuts are a familiar part of UK winters. Storms Arwen and Eunice in 2021/22 left thousands of homes without power. In a regional worst-case, most customers would be reconnected within hours, though remote or badly damaged parts of the network can take longer — in some cases, weeks.
A nationwide failure of the transmission system has never happened in Great Britain, and the Register describes the likelihood as low. If it did, impact would be severe, and full restoration could take up to seven days. For ordinary planning, a torch, a radio, a charged power bank and a way to stay warm are the useful habits.
Source: National Risk Register 2025, risks 26b and 26a.
Flooding
Worst-case: significant impact, 1–5%
Coastal, river and surface-water flooding are among the more familiar serious hazards in the UK. The reasonable worst-case for each is rated significant impact, with a 1–5% chance of that worst-case in five years. Surface water flooding can arrive with little warning.
Impacts can include damage to homes, a need to evacuate, and days or weeks without electricity, phones or mains water in the worst cases. The practical steps are quieter: know your flood risk, sign up for Environment Agency warnings, and keep a small bag ready if you are ever asked to leave.
Source: National Risk Register 2025, risks 51a, 51b and 51c.
Cold snaps
Worst-case: significant impact, 5–25%
A severe week of lying snow and very low temperatures — the sort of spell nicknamed the “Beast from the East” in 2018 — is rated significant impact, and is one of the more likely worst-cases on this list (5–25% over five years). Homes can become cold quickly when the heating goes off.
Transport, schools and some power or water supplies can be disrupted. Warm clothing, blankets, a torch and a way to get official updates matter more here than specialist equipment. Check on neighbours who may need a little extra help.
Source: National Risk Register 2025, risk 50.
Water outages
National worst-case: minor impact, 0.2–1%
Burst mains and short local outages are fairly ordinary. The Register’s reasonable worst-case — the sudden loss of piped drinking water from treatment works in one region — is assessed as a minor national impact, with a 0.2–1% chance in five years. Water companies plan to provide an alternative supply as soon as possible, and within 24 hours.
Even so, official advice is to keep bottled water at home: three litres per person per day for drinking, so nine litres per person for three days, and more if you need it for washing, pets or formula. That covers the gap before a bowser or bottled-water station is in place.
Source: National Risk Register 2025, risk 39; Be Ready checklist.
Network or bank outages
Worst-case: moderate impact, 1–5%
Storms can take down mobile and landline connections together. The reasonable worst-case of a regional loss of fixed and mobile communications is rated moderate impact, with a 1–5% chance in five years. Landlines may stay offline for several days if there is no power at the premises or cables are damaged. Storms Arwen and Eunice are recent examples on a similar scale.
A technological failure at a major retail bank is rated the same: moderate impact, 1–5% over five years. A battery or wind-up radio, some cash in mixed notes and coins, and important phone numbers written on paper are the calm, useful precautions. Contactless and mobile banking are convenient, not a guarantee.
Source: National Risk Register 2025, risks 25 and 31a.
Impact labels (minor, moderate, significant, catastrophic) follow the Register’s five-point scale. They describe a national planning scenario, not how serious an event would feel in one household.
