Leyton has a moderate flood risk, and most of it comes from rain. Only a thin slice of the town is in the river flood zones. About one postcode in eight is rated high on at least one flood measure. Only a handful of homes face a high risk from the river itself. The marsh the town was built on still gets a say.
On the Environment Agency's river-and-sea flood maps, about 2% of Leyton's postcodes are in flood zone 3, the highest-probability band. Another 9% are in zone 2, the medium-probability fringe beyond it. The Agency's register holds 26 recorded flood events for the area. The most recent was in December 1947, when a main river overflowed a channel that had no raised defences. The ground is lowest along the Lea on the western edge, where the town rises out of the old marshland, so that is where a river has always had the first say.
Surface water is not part of those zones. The river-and-sea maps model water coming out of a channel. Heavy rain collecting on streets and back gardens is measured separately, and in a town this built up it is the more common way for water to reach a front door.
With the Environment Agency's allowance for a wetter climate, about 13% of Leyton's postcodes fall inside the flood zone. That is the Agency sketching the future in pencil and admitting the lines will move.
For most of Leyton, buildings insurance should be routine. The homes on the high-risk lists are where premiums and excesses start to reflect the map. A terrace on the low ground near the Lea and an identical one on the slope up towards Whipps Cross look like the same house to a buyer and two different risks to an underwriter.
Measured by postcode, counting rivers, sea and surface water together, about 12% of Leyton's postcodes are rated high on at least one of those measures, 24% medium and 54% low. A postcode needs only one of the measures to flag it, so these shares run wider than the river zones alone.
Counting homes gives a narrower figure. The Environment Agency's rivers-and-sea mapping lists 3,284 properties in Leyton, drawn only from the 83 postcodes with some risk at all. Of those, 29 are at high risk, 535 medium, 1,492 low and 572 very low. Only seven of the high-risk properties are homes. The useful check is to enter the exact address in the Environment Agency's long-term flood risk service, which takes less time than a second viewing.
On defences, about 1% of postcodes fall inside the high-risk flood extent with no defence in the model, and about 2% inside it with a defence present. "Defended" means the Agency's model includes a wall or embankment. It doesn't mean the water stays out. A seller who mentions the defences is describing a model, and a model has never kept anyone's kitchen dry.
The nearest tide gauge with a long record is at Portsmouth, where sea level rose about 2 millimetres a year between 1962 and 2023. That measures how far Leyton is from the sea better than it measures anything about the Lea.
Leyton's flood risk is middling. The river threat is small and concentrated near the Lea, the wider risk comes from rain, and the answer for any given home depends on which list its address is on.