FFTP is biased in favour of the party with the largest share of the vote, or perhaps another way of putting is that the relationship between vote share and number of MPs is not linear.
And beyond this, the British electoral system has consistently favoured Labour for decades (as Boundary Commission changes fall behind demographic change and population movement)
https://www.independent.co.uk/voices/boundaries-review-bias-...
I can't see anything that disputes the claim "The Tories are the clearest benefactors" of the UK's electoral system.
The author makes a repeated assertion that boundaries are currently biased "15 seats" against the Tories, but I cannot tell where this number is coming from.
The fact remains that the Tories have won the last few elections by receiving a disproportionate number of MPs relative to their vote share. Moreover, polling suggests that they will continue to have the highest vote share.
Have you considered adding elections when the Conservatives didn't win the most votes to your data set?
1. The Conservative party has proposed some new boundaries.
2. The new boundaries would have given the Conservatives 15 extra seats, according to the 2017 vote share.
3. The current boundaries are very out of date.
4. The new boundaries follow stricter rules about constituency size variation.
5. The new boundaries lead to a reduced number of MPs.
6. 3-5 imply that the new boundaries are fairer than current boundaries.
7. 2 and 6 imply that the current boundaries are biased 15 seats towards Labour.
The hole is in statement 6; points 3 and 5 are irrelevant to the question of fairness and point 4 is weak as there are plenty of ways to gerrymander the boundaries whilst equalising constituency size. What's "utterly bizarre" is that Rentoul expects many people to swallow such a flawed argument.