A number of people have pointed me in the direction of comments made the other day by former Tory strategist Andy Maciver, who claimed that if SNP voters didn't switch to the Greens on the list, the Tories could gain extra seats without even needing to make any progress in terms of votes. His reasoning was that the SNP's dominance at constituency level means they won't win many list seats, and "those seats have got to go somewhere".
For the avoidance of doubt, that claim is utter gibberish. It's not even one that most advocates of tactical voting would make, because it's not merely untrue - it's actually the complete opposite of the truth. SNP dominance at constituency level would make it harder for the Tories to win seats, not easier. If, hypothetically, the SNP were to win all 73 constituency seats, that would self-evidently leave all of the opposition parties severely under-represented at constituency level. The d'Hondt method kicks in at that point and tries to resolve the under-representation by distributing list seats in a compensatory way. But here's the thing - there are only 56 list seats to go round. Yes, they've got to go somewhere, and they'll be spread thinly among all of the major opposition parties, all of whom will have been wiped out in the constituencies. There simply won't be enough to make up the shortfall, and in all probability the Tories will end up with fewer seats than the d'Hondt principle really entitles them to.
It's a very simple calculation : if the SNP "break the system" and get more seats than they should, the opposition parties are bound to get fewer seats than they should. For some reason, Maciver has either completely misunderstood that calculation or is misrepresenting it.
And that's really the interesting question here - what is his motivation? Is this an example of the political dark arts, with Maciver seeking to use reverse psychology to persuade SNP supporters to give their list votes to small parties, and thus potentially help the Tories if those votes turn out to be wasted? Or is he just indulging in wishful thinking based on a genuine misunderstanding of how the electoral system works?
As ever, answers on a postcard, folks...