Yes, Battersea is at risk. On the official map most of it is flood plain, and it stays dry because the Thames is held back. Most of its postcodes are in the highest river-and-sea flood zone. Rain adds a second way in. When the Environment Agency rates individual homes, only a few dozen come out at high risk. The map shows the land as low-lying. The defences are what keep it dry.
The Environment Agency puts about 63% of Battersea's postcodes in flood zone 3, the band with the highest probability of flooding from rivers or the sea. A fraction of 1% are in flood zone 2, the medium-probability band. The two zones do not overlap, so zone 2 is only the strip that falls outside zone 3, and here there is almost no such strip. Battersea grew up by draining marsh along the tidal Thames, and the zone map still shows the marsh.
Surface water is a separate risk from the river. It depends on rain landing faster than the drains can carry it away, and on a district this built-up there are few gardens to soak it up. The Agency's surface-water mapping is not given as its own share here. It is counted within the postcode measure further down.
The Environment Agency's climate-adjusted map, which allows for future changes in river and sea levels, puts about 65% of postcodes in the higher zones. That is two points more than today, on land where most of the map is already shaded.
Insurance is where the zone map costs money. Insurers price by address, and a zone 3 postcode prompts questions about the floor level, the basement and whether the ground floor has ever flooded. A converted lower-ground flat will be priced quite differently from the fourth floor of the same building. Get an actual buildings-insurance quote for the exact flat or house you are buying, because that is the figure you will pay for as long as you live there.
Counting every measure together, river, sea and surface water, about 18% of Battersea's postcodes are rated high risk on at least one, about 25% medium on at least one, and about 46% low on at least one. A postcode only needs to score on one measure to be counted, so these shares say how widespread some level of exposure is. They do not show how severe it is.
The figure that matters most to a buyer counts homes. In its rivers-and-sea assessment, the Environment Agency lists about 19,900 properties in the Battersea postcodes that carry any risk at all; postcodes with no risk are left off the list. Of those properties, 72 are rated high risk, 66 of them homes, none medium, 943 low and about 16,800 very low. Seventy-two is a small and specific number. What matters is whether the flat you are viewing is one of them.
The defence question explains why the zone map and the property count differ so much. About 7% of postcodes fall inside the high-probability flood extent with no defence in the Agency's model, and a fraction of 1% fall inside it with a defence modelled. In the model, "defended" means a wall or barrier is drawn on the map between the water and the street. A wall on the map is a promise someone has to keep maintaining.
The sea-level figure comes from the nearest tide gauge in the record, at Portsmouth. Between 1962 and 2023 it measured a rise of about 2 millimetres a year. That gauge is on the south coast, a long way from SW11, but it is the measured rate on offer.
Battersea's flood risk is high, and pointing to how few homes are rated high risk does not remove it. The danger comes from the river, it is mapped across most of the district, and the defences keeping the water out have to keep doing that job for as long as you own the home.