Filton's flood risk is a rain problem, not a river problem. The rivers and the sea barely feature here. What does feature is surface water, the kind that arrives when heavy rain falls faster than the drains can take it, and on that measure the suburb scores badly. About a third of postcodes carry some high surface-water risk. That is the number that matters, and it is the reason to read a specific street carefully before you commit to it.
Start with the reassuring half, because it is genuinely reassuring. Formal river and tidal flood exposure is close to nothing. Only about one postcode in fifty sits in the medium river-and-sea flood zone, and effectively none falls into the highest river-and-sea zone. Six miles inland and well above any tidal reach, Filton was never going to flood from a swollen channel, and the maps confirm it. If your worry is a river coming over its banks, this is not the place that keeps you awake.
Surface water is where the honesty is required. About a third of postcodes carry a high surface-water flood indicator, a further third sit at medium, and roughly six in ten touch some level of risk once you include the low band. This is the drainage-and-downpour story: hard rain landing on a built-up interwar suburb with a lot of roof, road and hardstanding, and pooling wherever the ground and the gullies cannot clear it fast enough. It does not threaten the whole area evenly, and it varies street to street, which is exactly why the postcode-level average understates the problem for some addresses and overstates it for others.
The forward look does not add a new threat, which is worth stating plainly. The climate-adjusted river-and-sea flood zone covers effectively none of Filton, so the projections that account for higher future sea levels and heavier flows do not pull the suburb into the river-and-sea danger zone. The risk that exists today is the surface-water one, and it is the surface-water one that a buyer should plan around, not a future coastal threat that the data does not support.
For insurance, the practical effect is real without being catastrophic. A high surface-water indicator on a specific address can push premiums up, prompt an insurer to ask for more detail, or lead to a higher excess on the flood portion of a policy. It is the sort of thing that is manageable when you know about it in advance and awkward when it surfaces during a purchase. Get a flood search on the actual property, ask the current owner whether water has ever pooled near the door, and price any answer into the offer rather than the mortgage.
Filton scores at the bottom of the flood scale, and the reason is surface water rather than rivers. Treat it as a drainage risk to check street by street, not a reason to walk away, and never buy here without confirming what the rain does to the specific address.