These are the notional results of the 2019 United Kingdom general election if it had taken place under the new constituency borders used from the 2023 Periodic Review of Westminster constituencies, as calculated by Michael Thrasher and Colin Rallings. In constituencies whose borders have changed, precise results under the new boundaries usually cannot be known as election results are not usually reported for subdivisions of constituencies. However, it is possible to estimate what the election results would have been by extrapolating from local election results for which more granular data is known.[1][2]
Most news organizations including the BBC use these notional results for statistical purposes such as when calculating the swing from the 2019 general election to the 2024 general election by constituency.[3]
The "Change" column is an index used by Thrasher and Rallings to refer to how radically the borders of the constituency in question changed in the boundary review. "None" is no change in the borders (therefore the notional results are identical to the actual results), a small number denotes little change, and a larger number denotes more change.