Notional results are estimates of what a past election outcome would have been if it had been contested under a different set of constituency boundaries. They are not actual results, but statistical reconstructions produced when electoral boundaries are redrawn. In the United Kingdom, notional results are most commonly used after a periodic review of parliamentary constituencies by the boundary commissions for England, Scotland, Wales and Northern Ireland.
Where notional results sit in the UK geography system
In the UK, every address and postcode belongs to a specific electoral geography, such as a parliamentary constituency, a ward for local government, or a polling district. When boundary changes are introduced, the old constituencies are replaced by new ones. A notional result takes the votes cast in the former, smaller areas and reassigns them to the new constituencies as if the election had been fought there. This is done by aggregating voting data from the most local level available, typically polling districts or, more recently, the postcode-based output areas from the census.
How it relates to postcodes and addresses
Postcodes are the key unit for this work. Each postcode in the UK is linked to a specific polling district or ward. The boundary commissions use postcode data to map the precise area covered by a constituency. When they produce notional results, they take the actual votes recorded for each postcode or address-based area and calculate what the result would have been for the new set of boundaries. This means that if you look up a postcode on a site like Postcodes UK, you may see a notional result alongside the current constituency. It tells you, for example, that in the 2019 general election the area around your postcode would have returned a certain party, even if the actual result in 2019 was for a different constituency.
Why it matters to someone researching an area
For someone researching a neighbourhood, notional results are important because they provide a consistent way to compare political trends over time. Without them, a change in boundaries would make it impossible to tell whether a shift in votes was due to a genuine change in public opinion or simply because the area had been merged with a different one. They are also used by journalists, analysts and campaigners to understand how a place might vote in the next election. For example, if you are looking at a set of postcodes in a newly drawn constituency, the notional result gives you the best available estimate of the political baseline. It is not a prediction, but it is the closest thing to a historical record for the new shape of the seat. In summary, notional results help bridge the gap between old and new electoral maps, using postcode-level data to keep comparisons meaningful.