Mostly no. The risk in the City of London runs along the Thames and stops there. About one postcode in twenty is in the river's highest flood zone. Only three properties are rated high risk, and none of them are homes. For a district built on the river, it stays fairly dry.
The Environment Agency's river-and-sea mapping puts about 5% of the City's postcodes in Flood Zone 3, the highest-probability zone, and about 1% more in Flood Zone 2, the medium-probability band just beyond it. The two zones don't overlap, so the second figure sits on top of the first and isn't part of it. The Agency's records list 65 flood events in the area, and the most recent dates from 1928, when the main river overtopped its defences. Nobody has seen the Thames come over the top here for almost a century, and people living in the riverside postcodes have mostly stopped thinking about it.
Surface water is the part the river zones leave out, and the City has very little ground to absorb it. Gardens cover about 2% of its area, and the rest is buildings, pavement and roads.
The Environment Agency also models a version of the zones with an allowance for climate change. On that map, about 8% of postcodes fall inside the flood zones. That is the Agency's planning scenario for future rainfall and sea levels, so its share is larger than today's.
Insurance for most City flats should be ordinary. A riverside block in the top zone is a different conversation, and so is any home on a ground floor or below it, since that's where water would reach first. So for any riverside flat, ask an insurer to quote for that specific flat and floor, because a block on the river can be in Flood Zone 3 while the flats upstairs are never troubled by it.
On the broader postcode indicators, which count a postcode if it rates high on any of several measures, surface water included, about 3% of City postcodes rate high, about 4% medium and about 9% low on at least one measure.
Counting properties tells you more. The Environment Agency's rivers-and-sea risk register lists 603 properties across 47 City postcodes, and only postcodes with some risk appear on it at all. Of those properties, 3 are rated high, none medium and none low, and 496 are rated very low. None of the high-risk properties are homes. "Thames-side" sells a City flat well, but the register shows the river is a view for these buildings and hardly ever a threat.
On the Agency's flood-extent modelling, about 2% of City postcodes fall inside the high-risk extent with no defence in the model, and less than 1% fall inside it with a defence modelled. "Defended" only means a defence appears in the model. It says nothing about whether that defence would hold on the night, and the 1928 flood came over the top of defences that were already there.
The nearest tide gauge in the national record is at Portsmouth, which measured a rise of about 2 mm a year between 1962 and 2023. That is a long way down the coast, and it describes what that gauge measured over those years.
The City's flood risk comes out middling overall. Nearly all of it is dry, but the riverside strip is where the risk is real, and that strip includes some of the most attractive addresses.