I pointed out the other day that just about the only thing that might be more outrageous than ITV's decision to hold a two-party election debate in a multi-party democracy would be for Jo Swinson to get her preferred outcome and for there to be a three-way debate in which the fourth-largest Commons party is included and the third-largest is excluded. But Sky News have proved up to that task - they've brazenly invited the leader of a party with 20 MPs (Swinson) and not invited the leader of a party with 35 MPs (Sturgeon). Like ITV's decision, this is an entirely arbitrary selection based on the broadcaster's own preferences and not on objective criteria. It most certainly is not justified by precedent, because Nicola Sturgeon was invited to every leaders' debate in 2015, even though the SNP went into that election as only the fifth largest Commons party and the Lib Dems went in as the third-largest. (And the SNP were not obviously doing better in the opinion polls in 2015 than they are now, so that's no excuse either.)
The broadcasters are quite literally making up the rules as they go on, which is the sort of thing you'd expect to happen in Putin's Russia - and the likes of Andrew Neil would be quick to scream about it if it did. My own view is that there should be a moratorium on leaders' debates until an independent body can come up with objective criteria for inclusion and exclusion that are applied consistently, not changed at a whim because broadcasters are prioritising "box office potential" over the integrity of the democratic process.
I also cannot understand why the SNP are being so passive at the moment. I know they were bruised by a failed legal challenge to the three-way debates in 2010, but they have a much stronger case now as the third largest party, and you can't win a raffle if you don't buy a ticket.
UPDATE: I see Sky's carefully-worded justification for excluding the third-largest party is that they have invited "the three main UK-wide parties". Guys, when you're in a hole, it's generally best to stop digging. "UK-wide" is not a synonym for "based in London". Neither Labour nor the Liberal Democrats are UK-wide parties because they don't put up candidates in Northern Ireland. If you want a debate between UK-wide parties only, it'll be a Boris Johnson monologue. (Although maybe I shouldn't put ideas in their heads, because they'd probably be tempted.)