Yes, in places, and mostly from rain rather than rivers. The main river-and-sea flood zones barely reach the town. Count every measure, though, and about one postcode in seven comes out at high risk on at least one of them. Some streets are dry and others aren't, and the difference can be a matter of yards.
In the Environment Agency's river-and-sea flood zones, about 1% of Sidcup's postcodes fall in Flood Zone 3, the highest-probability band. Another 1% fall in Flood Zone 2, the medium-probability fringe beyond it. The two zones don't overlap, so Zone 2 is the extra ring and has nothing to do with the core. By that measure, Sidcup is a long way from a flood town.
Rivers and the sea aren't what catches people out. Surface water is rain that falls faster than the ground and drains can take, and the river zones leave it out entirely. The Environment Agency holds eight recorded flood events here. The most recent was in 1977, when a main river overflowed a channel too small for it, and about 1% of postcodes lie within a historically flooded area. The rivers have been on good behaviour for decades. Rain hasn't signed the same agreement.
The Environment Agency's climate-adjusted zone, which models how the river-and-sea risk could grow, takes in about 2% of Sidcup's postcodes. That is still small, and it is a modelled scenario.
Insurers price on the exact address and the measure that applies to it, and surface-water risk shows up in quotes even where the river map is clean. A quote is cheap to get and worth getting early, because a house that's hard to insure is also a house that's hard to sell.
The wider postcode measure counts a postcode if it rates at risk on any one of several indicators, surface water included. On that basis, about 15% of Sidcup's postcodes rate high on at least one, 16% medium and 31% low. That is a much less comfortable picture than the river zones alone give. The risk is spread across the town and varies from one street to the next.
The Environment Agency's rivers-and-sea mapping counts actual properties, which is more useful. Only 21 postcodes in Sidcup carry any of that risk, covering 425 properties between them. Of those, 142 are rated high risk, 105 of them homes. None are rated medium, 44 are low and 51 very low. Most of Sidcup's postcodes don't appear on that list at all, and the ones that do have a problem worth taking seriously.
The modelled high-risk river-and-sea extent covers about 2% of postcodes with defences included and the same 2% without them. "Defended" only means a defence exists in the model, and here it doesn't shrink the high-risk area at all. Nothing in the model is holding the water back from those homes.
The nearest tide gauge is at Dover, where the sea rose by about 2 millimetres a year between 1961 and 2010. The gauge is far enough away to show that the sea is a minor concern for Sidcup. The rain on its roads is a bigger one.
Sidcup's flood risk is below average because surface water reaches more streets than the river maps admit. Search the Environment Agency's long-term flood risk service by the exact house number, surface-water layer included, before you pay for a survey.