West Drayton has a modest river problem and a bigger rain problem. Very few postcodes are in the river-and-sea flood zones. Around one postcode in six rates high on at least one flood measure. A little over a hundred homes face a high chance of river flooding. Most of the risk here comes from rain on hard ground.
On the Environment Agency's river-and-sea mapping, about 1% of West Drayton's postcodes are in Flood Zone 3, the highest-probability band, and about 3% are in Flood Zone 2, the medium-probability fringe beyond it. The two bands don't overlap, so together they cover a small slice of the town. The Environment Agency has one recorded flood event in the area, in January 2003, when a main river overflowed its channel at a point with no raised defences. The town lies near the Colne Valley, and the river risk follows the low ground along it.
Surface water is the bigger story. Surface-water risk does not show up in the flood zones at all, which deal only with rivers and the sea, so a postcode can be clear of both zones and still sit low enough to collect what the drains cannot take. In a town of post-war estates, car parks and a motorway along its southern side, heavy rain has fewer places to soak away than the river maps suggest.
Allowing for a changing climate, the Environment Agency's climate-adjusted flood zone takes in about 9% of postcodes. That is a modelled estimate of how far the zone could spread under future conditions, and the line on the map is drawn by a model; no date is attached to it.
For insurance, most of West Drayton should be routine to cover, and the cost is likely to depend on the exact property more than the postcode. A home on a street that carries a high surface-water rating can still draw higher premiums or a higher excess, and an insurer's own map decides that, whatever the river zones say. Put the exact address into the Environment Agency's long-term flood risk service and read the surface-water result separately from the rivers result, because the two can disagree on the same front door.
Counting every measure at once, about 17% of West Drayton's postcodes rate high on at least one flood indicator, about 25% rate medium and about 49% rate low. Those shares include surface water alongside rivers and the sea, so a postcode counts if any one of several measures flags it. That is a broader net than the flood zones, and it explains why the town looks safe on one map and much less safe on another.
Counting homes gives a clearer picture of who is exposed. The Environment Agency's rivers-and-sea mapping lists 1,231 properties in the 45 postcodes that carry some river or sea risk. Of those, 135 are rated high, 55 medium, 316 low and 101 very low. Postcodes with no river or sea risk at all are left out of that count entirely, so the total describes the exposed streets and nothing else.
On defences, about 0.5% of postcodes fall inside the Environment Agency's modelled high-probability flood extent where no defence is present in the model, and about 0.8% fall inside it where a defence is present. A defence in the model means something is built there and has been allowed for in the modelling. Defences can be overtopped, can fail and need maintaining, so "defended" says what is in place, and a buyer should not read it as a promise about the living room.
The nearest tide gauge on record is at Portsmouth, where sea level rose by about 2 millimetres a year between 1962 and 2023. That is a measured rate at a gauge on the south coast, a long way from West Drayton. The sea is the one flood source this town can safely leave to somebody else.
West Drayton's flood risk is worse than its flood zones make it look, because the rain does the damage the river mostly doesn't. Most buyers will be fine, and the rest need to know which street they are on.