Yes, North Weald Bassett has real flood risk, and the river maps show only part of it. Fewer than one postcode in ten is in the highest river flood zone. About three in ten score high once every type of flooding is counted. The climate-adjusted zone takes in about one in five. The village stands on the highest ground in its parish, and the water still finds its way in.
Start with rivers and the sea. In the Environment Agency's river-and-sea flood zones, about 9% of North Weald Bassett's postcodes are in Flood Zone 3, the high-probability band, and another 11% are in Flood Zone 2, the medium-probability fringe just beyond it. The two zones do not overlap, so the second figure is extra ground, not a larger area that contains the first. The Environment Agency has 15 recorded flood events for the area, and about 13% of postcodes fall within its historic flood record. The latest recorded event was in December 1993, when a main river overflowed its channel with no raised defences in the way.
Surface water is the part those zones leave out. Rain that cannot drain away does not show up in a river-and-sea zone at all. In North Weald Bassett it only appears in the combined postcode measure further down, and that measure explains most of the difference between the two sets of numbers.
The Environment Agency also models how the river zones grow under a changing climate. On that projection about 20% of postcodes fall inside a flood zone. It is a modelled outline of where the water could reach, and nobody has set a date for it.
Insurance follows the risk. Homes in the high-risk postcodes can expect fewer insurers willing to quote, higher premiums and bigger excesses than a house on drier ground in the same village. Two houses a few streets apart can sit in different flood bands and end up with quite different policies. Get an indicative buildings-insurance quote for the exact address while the survey is still being booked, because the insurer's answer is the most practical flood report a buyer can get.
The broadest measure checks each postcode against several flood indicators at once: rivers, sea and surface water. On that basis about 30% of North Weald Bassett's postcodes rate high on at least one indicator, about 32% medium and about 55% low. A postcode only needs one bad measure to make the high list. That is why this figure is so much bigger than the river zones.
Counting homes is more useful than counting postcodes. The Environment Agency's rivers-and-sea mapping lists 718 properties across the postcodes that carry any risk at all. Postcodes with no risk are left out entirely. Of those 718, 32 are at high risk, all of them homes, five at medium risk, 115 at low risk and 134 at very low risk. "Low" here still means a small chance of flooding in any given year. It does not mean none.
On whether anything holds the water back, the modelling is fairly clear. About 9% of postcodes are in the high-risk river extent with no defence modelled. Only about 1% are in the high-risk extent with a defence present in the model. "Defended" in that sense means a flood wall or bank appears in the model. Nobody has promised it will hold back a particular flood, and it is the word a seller would most like to say first.
Flood risk is North Weald Bassett's poorest showing, with three postcodes in ten flagged high on some measure and little modelled defence in the way. Buyers here should choose the exact house with the flood map open, because the village average will not help much.