This page allows you to make your own predictions both for the entire country and for any particular Westminster constituency in England, Scotland and Wales. All you need is your own estimate (or guess) of national opinion support for the main parties.
There is also a Regional Predictor for non-uniform swings and a separate predictors for Scotland and Northern Ireland.
To make your prediction, enter the national (GB) support levels for the main parties. (The actual election results are shown for reference.)
Advanced options: you can also enter party support figures for Scotland, including the SNP; as well as tactical fractions (usually between 0% and 50%).