Methodology - Projected Outcome with Tactical Voting

For the methodology behind our tactical recommendations, please see our Methodology and Data pages.

2019 implied results using new boundaries are sourced from Professors Colin Rallings and Michael Thrasher for Sky News, the BBC, ITV and the Press Association

To calculate the progressive tactical vote needed to win a seat we do the following:

  1. Check the progressive tactical vote for the seat in question based on our own advice
    • In cases where we have no specific tactical voting advice, we take the largest progressive party (Labour, Lib Dems, Green, SNP or Plaid) according to our average of recent MRPs. We may have no specific tactical advice because we recommend voting for your preferred party, because the seat is too tough to call between multiple progressive parties, or because voting advice is TBC.
  2. Check the largest regressive party (Conservative or Reform) according to our average of recent MRPs
  3. Apply a "pessimism factor" of 0.5% - subtract this from the progressive party vote share, add it to the regressive party vote share
  4. Calculate the regressive lead over the recommended progressive party
  5. Calculate the total vote share of the other progressive parties
  6. Calculate what proportion of voters for the other progressive parties would need to switch their vote to the recommended progressive to beat the biggest regressive party
A worked example - East Wiltshire
ToryLabourLib DemGreenReformOther
You Gov MRP - 2024/06/1934%31%8%6%19%1%
IPSOS MRP - 2024/06/1836%32%12%4%14%0%
Survation MRP - 2024/06/1432.75%31.56%15.73%5.81%12.67%1.48%
Simple Average34.25%31.52%11.91%5.27%15.22%0.83%
  1. Our tactical advice here is Labour on an average of 31.52%
  2. The biggest regressive party (Conservative or Reform) is Conservative on an average of 34.25%
  3. Apply a 0.5% "pessimism factor" to get Labour on 31.02% and Conservative on 34.75%
  4. The regressive lead is 34.75% - 31.02% = 3.73%
  5. Calculate the total vote share of other progressive parties - in this case, Lib Dem (11.91%) plus Green (5.27%) to get 17.18%
  6. Calculate the proportion of of voters for other progressive parties would need to switch their vote for Labour to win. In this case, 3.73 / 17.18 * 100 = 21.71 percent of other progressive voters, which we round up to 22%.

If we now assume 22% of Lib Dem & Green voters back Labour, we can see Labour would beat the Conservatives: