Yes, on the Environment Agency's maps Southwark is about as exposed to flooding as a district can be. Nearly every postcode is in the highest river-and-sea flood zone. With climate change allowed for, all of them are. Take the river walls out of the model and two in three postcodes fall inside the high-risk flood extent. Put the walls back and almost none do. What keeps Southwark dry is the defences, and on the official maps the defences are also the whole of the risk.
The Environment Agency puts about 93% of Southwark's postcodes in flood zone 3, its highest river-and-sea band. Another 4% are in zone 2, the medium-probability fringe outside zone 3. Those zones describe the land, and here the land is the old floodplain. Before the river was walled in, Southwark was mostly marshy tidal islands crossed by a narrow strip of firmer ground. The Romans built their bridge on that strip, and the zone map still remembers the marsh around it.
The zones only cover rivers and the sea. Surface water is the rain that runs off roofs and roads faster than the drains can take it, and river defences do nothing to stop it. In the Environment Agency's postcode indicators it's counted alongside river and sea flooding, and it makes up part of the picture further down this page.
With the Environment Agency's allowance for climate change added, 100% of the area's postcodes fall within the flood zones. That's the agency's planning view of where the water could reach as conditions change.
Insurers price cover address by address. A postcode deep inside zone 3 gets looked at more closely than one on high ground, even when the building is a fourth-floor flat. Most homes here are flats in blocks, so the cover usually comes through the building's own policy. Ask early for the block's buildings insurance schedule and its flood history, because the freeholder's insurer will already have formed a view of the river.
Combining every measure the Environment Agency publishes for postcodes, surface water included, about 10% of Southwark's postcodes rate high on at least one of them, about 13% medium, and about 31% low. A postcode counts if any single measure flags it, which is why these shares sit apart from the zone figures above.
Counting properties tells a calmer story. The Environment Agency's rivers-and-sea assessment lists 43,056 properties across the postcodes that carry some risk, and postcodes with none don't appear at all. Of those, 33 are rated high risk, none medium and none low, and around 41,240 very low. None of the 33 high-risk properties is a home. The map that ignores the walls floods almost the whole district. The one that counts them finds 33 properties and not one bedroom.
The defences explain the gap. About 67% of postcodes fall inside the high-risk extent when the Environment Agency models the area with no defences, and under 1% when it models them in place. "Defended" means a defence appears in the model, and it says nothing about whether a particular property stays dry. The Agency holds 357 recorded flood events for the area. The latest, from 1928, was the main river overtopping its defences, which shows defences here have been beaten before.
The nearest tide gauge with a long record is at Portsmouth, where sea level rose by about 2 millimetres a year between 1962 and 2023. That is what the gauge measured over those years, on a coast a long way from Bankside.
Southwark's flood risk is poor. The district lies on floodplain that the river walls have kept dry for nearly a century, and anyone buying here is relying on those walls.