Islington has no river or sea to worry about, but it does get water from the sky. None of its postcodes is in the official river-and-sea flood zones. Even so, about one in five carries a high flood rating on at least one measure. That comes from rain with nowhere to go, not from a river bursting its banks. On the river maps the place looks bone dry, and on the full set of measures it does not.
The Environment Agency's river-and-sea mapping puts 0% of Islington's postcodes in Flood Zone 3, the highest-probability band, and 0% in Flood Zone 2, the medium-probability band beyond it. Islington is built on a hill, and for centuries that hill sent water down to the City through springs and wooden pipes. Rivers and the sea are not the issue here.
Surface water is the issue. When heavy rain hits roofs, roads and paved-over gardens faster than the drains can carry it away, it pools on the low points of streets and runs into whatever sits below pavement level. A borough made mostly of hard surfaces gives that water very little ground to soak into.
The Environment Agency's climate-adjusted mapping, which models how the river-and-sea zones might look under future conditions, also puts 0% of postcodes in them. Even in the projections, the rivers stay away.
For insurance, a home outside the river-and-sea zones usually has fewer questions to answer, but insurers price the individual address and many of them now check surface-water risk too. Get a quote on the actual flat while you still have time to walk away. If it is a lower-ground-floor or basement flat, ask the seller directly whether water has ever come in, because that is the level surface water reaches first.
The postcode indicators look at several measures at once, including surface water as well as rivers and the sea, and a postcode is counted if it reaches a given level on any one of them. On that basis, about 19% of Islington's postcodes rate high on at least one measure, about 25% rate medium and about 45% rate low. With nothing on the river maps, the high ratings come from the other measures, and rainfall is the one this hill has never been able to shed.
The Environment Agency's modelled flood extents show 0% of postcodes in the high-risk river or sea extent, whether defended or undefended. A flood wall is not needed where the river-and-sea model finds nothing to hold back, and neither figure says anything about rain falling on the street.
The nearest tide gauge in the record is at Portsmouth, a long way from Islington. Between 1962 and 2023 it measured sea level rising by about 2 millimetres a year. That is a fact about the south coast's water level over that period, and it has nothing to do with whether an Islington basement takes in water.
There is no historic flooding recorded in the area, with 0% of postcodes inside a recorded flood outline. That is reassuring, but it only means nothing has been officially recorded. Surface-water flooding tends to be brief and local, and it is often recorded only by the person mopping up.
Islington is safe from rivers and the sea, but its flood risk is still weaker than the river maps make it look, because heavy rain does real damage here. The risk depends on the building, and the flat below street level carries most of it.