Yes, Tilbury is about as exposed to flooding as an English town gets, built on old Thames marsh with nearly every postcode in the highest river-and-sea zone. Allow for a changing climate and it is every postcode. The worst flood on record came in off the sea. What stands between the town and the water is a line of defences, and the different measures give those defences very different amounts of credit.
On the Environment Agency's river-and-sea flood map, about 93% of Tilbury's postcodes are in Flood Zone 3, the highest-probability band, and about 7% are in Flood Zone 2, the medium-probability fringe beyond it. The two bands are separate, so between them they cover the whole town. Flood Zone 2 is the smaller number here because there is hardly any ground left over once Flood Zone 3 has taken its share. The river narrows to its tightest point along this stretch of Essex, and the town was laid out on the flat land beside it.
Surface water from heavy rain has no separate figure in this picture; it is folded into the postcode-level measure below, alongside rivers and the sea. What is on record is the history. The Environment Agency logs 88 recorded flood events across the area, with about 37% of postcodes inside a recorded flood outline, and the most recent came from the sea in February 1953.
The Environment Agency also draws a version of the zones that allows for climate change, and on that map 100% of Tilbury's postcodes fall inside. That describes how the modelled flood area grows as the climate shifts. It puts no date on any water arriving.
Insurance is where this turns into money. A home in Flood Zone 3 on a coastal marsh is the kind of property insurers look at closely, and premiums, excesses and even willingness to quote can vary sharply from one house to the next. Ask for a buildings insurance quote on the exact address as soon as a house makes the shortlist, and ask the seller whether any past claim or flood has been recorded against it.
Across the postcodes, about 88% rate high on at least one flood measure, with about 63% rating medium and about 63% low on at least one. Those shares count a postcode if any of several measures flags it, surface water included, which is why the same postcode can appear in more than one band. A single postcode in Tilbury can carry a high rating for one source of water and a low one for another, and both statements can be true at once.
The defence question is where the measures part company. On the Environment Agency's undefended flood extent, about 93% of postcodes fall in the high-probability area; on the version that shows defences present in the model, the high-probability share is under 1%. The agency's property-by-property assessment of risk from rivers and the sea, which takes defences into account, rates none of the 6,198 properties listed as high risk, six as medium, 117 as low and 6,043 as very low. Those numbers describe a town that depends heavily on its defences doing their job. "Defended" in that model means a wall or bank is drawn on the map, and a buyer reading it as a promise is asking a sea wall for more than it ever signed up to.
The nearest long-running tide gauge is at Dover, which recorded sea level rising at about 2.2 millimetres a year between 1961 and 2010. That is what the gauge measured over those years, at Dover, and it is the only sea-level record this answer draws on.
Flood risk is Tilbury's weakest point by a distance, with the whole town in the top zones and its safety resting on defences the maps can only partly vouch for. Buyers who can live with that, and can insure it at a price they accept, will find the rest of the place makes more sense.