Yes, Sheerness is at risk of flooding. Almost the whole town sits in the highest-risk river-and-sea flood zone. The sea has come over the defences before. Those defences are what keeps most homes at very low risk now. The risk is being managed rather than avoided, and if the defences stopped working, the managing would stop too.
The Environment Agency's river-and-sea mapping puts more than 99% of Sheerness postcodes in flood zone 3, the high-probability band. None fall in zone 2, which is the medium-probability fringe that lies beyond zone 3. There is no fringe here because almost everything is already in the top band. About 64% of postcodes also fall inside a recorded historic flood outline. The Environment Agency lists 185 recorded flood events for the area. The most recent, in February 1953, came from the sea when the defences were overtopped.
Surface water is a separate risk, caused by heavy rain with nowhere to drain. There's no separate figure for it here, but it's folded into the postcode measure further down. Every postcode in the town falls under the Lower Medway Internal Drainage Board, whose job is keeping the low ground drained. Flat ground on London Clay doesn't drain well, which is why that board exists.
The Environment Agency's climate-adjusted mapping also puts more than 99% of postcodes in the future flood zone. The current picture and the climate-change picture are the same because the town is already fully inside the zone, not because nothing is changing.
For insurance, a flood zone 3 address will be priced as one. Some insurers will quote higher premiums, higher flood excesses or both, and a few may not quote at all. Ask for a quote on the exact address before you instruct a solicitor. Ask the seller about past claims, and budget for the policy as a running cost of owning the house.
On this site's postcode indicators, which put surface water alongside rivers and sea, about 10% of Sheerness postcodes rate high on at least one measure, 27% medium and 62% low. Those bands overlap with the flood-zone figures above and measure something different, so the two sets shouldn't be added together or read as a contradiction.
Counted by property instead of postcode, the Environment Agency's rivers-and-sea assessment covers 7,129 properties. It puts 18 at high risk, 4 at medium, 292 at low and 6,792 at very low. Only postcodes that carry some risk appear in that count, so it's a list of homes the mapping is keeping an eye on, not a clean bill of health.
The defence modelling explains the gap between the two measures. Model the town with no defences and more than 99% of postcodes fall inside the high-probability flood extent. Model it with the defences and none do. "Defended" means a defence is present in the model. It doesn't mean your house is safe, and it doesn't say what state the defence is in on a given winter night. The sea wall is the one thing keeping Sheerness at the low end of that count.
About 59% of postcodes are within 500 metres of the coast, the threshold this measure uses. The nearest postcode is about 16 metres from the water, and the median distance is about 420 metres. In Sheerness, a sea view is included whether you wanted one or not.
The shoreline management plan's policy for this coast is to hold the line for the next 20, 50 and 100 years, meaning the stated intention is to keep maintaining the existing defences. That's a plan, not a contract. It depends on funding decisions that haven't been made yet, and a planning document has never stopped a tide.
The nearest tide gauge with a long record, at Dover, measured sea level rising about 2 millimetres a year between 1961 and 2010. That's a historic rate for that period, not a forecast. It's also the direction of travel the defences are built to cope with.
Flood risk is Sheerness's weakest point, and the rest of the town's case depends on it. Buy here knowing the whole town sits in the flood zone and relies on the sea wall to stay dry.