Yes, North Harrow has a real flood risk, but it comes from rain, not rivers. Almost none of it is in a river flood zone. A third of its postcodes still carry a high flag on at least one flood measure. A few dozen homes show up on the river maps at the highest level. Your risk depends on how a particular street drains, and the river maps do not show that.
On the Environment Agency's river-and-sea flood maps, about 1% of North Harrow's postcodes are in flood zone 2 and under 1% in flood zone 3. The two zones do not overlap. Zone 3 is the higher-probability band, and zone 2 is the medium-probability fringe outside it. On those maps alone, North Harrow looks dry.
The risk shows up once surface water is counted. That is rain that falls faster than the ground and the drains can take it, and it collects at low points in the roads and against back walls. With so little of the area in a river zone, most of the high flags further down this page come from surface water. The river maps do not show surface-water risk at all.
The Environment Agency's climate-adjusted river-and-sea zone, which allows for heavier future rainfall, covers about 1% of postcodes. On the river measure, the forward look barely moves.
Insurance follows the measure the insurer checks. A home outside the river zones but on a surface-water flag can still face questions, excesses or a higher premium. A home that has made a claim will face more. Get an indicative quote on the exact address early, and look up the surface-water layer on the Environment Agency's long-term flood risk service for it. That is the layer that matters here.
Across every flood measure taken together, rivers, sea and surface water included, about 34% of North Harrow's postcodes rate high on at least one of them. Another 34% rate medium on at least one, and 53% low. A postcode counts if any single measure flags it, so these shares overlap with each other. They are much larger than the river-zone shares because they count a different kind of water.
In the Environment Agency's rivers-and-sea property count, 47 properties are at high risk, 45 of them homes. Another 88 are at medium risk and 233 at low risk, out of 1,114 properties listed. Only postcodes with some river risk appear on that list at all. For a buyer, the useful question is whether the house you are viewing is one of those 47.
The Environment Agency's modelled flood extents put about 1% of postcodes in the high-risk extent with no defence in the model, and about 1% with one. "Defended" means a defence appears in the model. It does not mean water stays out of a particular kitchen. At low risk, about 2% of postcodes are undefended.
The nearest tide gauge is at Portsmouth, where the sea rose by about 2 millimetres a year between 1962 and 2023. North Harrow is a long way inland, and sea level has nothing to do with its flood risk.
There is no recorded historic flooding anywhere in the area. That is reassuring. But surface-water floods are often short and local, and they are not always recorded, so the absence of a record does not mean none has happened.
North Harrow's flood risk is one of its genuine weak points, almost all of it surface water from heavy rain. It is manageable, but only if you check the street and the exact house before committing.