What difference did the Brexit Party's decision to stand down in Conservative seats make to the result of the 2019 General Election?

Question

On the 11th of November - a month before the general election - the leader of the Brexit Party, Nigel Farage, announced that the party would not field candidates in seats that had been won in the previous 2017 GE by the Conservative Party. Clearly this helped the Tories to their largest majority since 1987 by not only ensuring that the pro-Brexit vote was not split in these constituencies, but also allowing the party to focus aggressively on target seats, rather than allocating resources to defending existing Tory seats.

How much of an effect did this decision have on the result of the election? Is the effect quantifiable using polls & statistics, or are we forced to rely on anecdotal evidence from party insiders and campaigners?

Answer 1

The true answer is that we won't know for sure because we can't know how many people in those constituencies would have voted for the Brexit Party. I'm sure someone has done a more rigorous analysis based on polling and demographic data.

I'll show one estimate. The Brexit Party contested 275 seats and got 644,257 votes for an average of 2342 votes. If we assume they would have gotten the same result in those districts and all their votes went from Conservative candidates then the Conservative Party would have lost 25 seats that they won with a margin of less than 2342 votes. In reality though, they would likely get more votes in those districts because they are more pro-brexit but not all their votes would be taken from the Conservative Party. So this is just an estimate and it is probably wrong but perhaps you won't find a better estimate out there.