Labour have held Inverclyde more comfortably than had seemed likely at the close of the campaign, but nevertheless there was a hefty fifteen-point surge in the SNP's vote, with the Liberal Democrats once again being squeezed almost to the point of embarrassment. Here is the full result -
Labour 54% (-2)
SNP 33% (+15)
Conservatives 10% (-2)
Liberal Democrats 2% (-11)
UKIP 1% (-)
That represents a headline swing of 9% from Labour to SNP, although as with the Holyrood election it seems likely that there was heavy movement from the Liberal Democrats to both SNP and Labour, with a middling shift direct from Labour to SNP.
I've noticed quite a few Labour-friendly online commenters suggest tonight that what this result shows more than anything is the difference between voting patterns for Westminster and Holyrood. Well, I have to say, I still don't buy that for a moment - unlike general elections, by-election campaigns for each parliament tend to be more or less interchangeable, and my guess is that a Holyrood by-election in the equivalent constituency would have produced a similar result. However, the contrary point of view is ironically a useful enough fiction for the SNP, so by all means let Labour peddle it if they really want to!
I always felt that Objective One for the SNP in this election was to avoid a Glasgow NE-style drubbing, and the inevitable subsequent headlines about "the bubble bursting". They've achieved that, although clearly a victory or a defeat that was narrower still would have been preferable. However, I don't think we should overlook how much more difficult it is to win safe Labour seats in by-elections when Labour are in opposition at both Westminster and Holyrood. It's not impossible to do so, but it's always going to be like trying to climb a down escalator, and therefore what happened in Inverclyde is certainly not directly comparable with the contests in the previous parliament when an unpopular Gordon Brown was still in Number 10. In time, this result could end up looking extremely creditable for the SNP - although in truth the long-term impact in either direction will probably be minimal.
Oh, and a final thought - the acceptance speech by the new Labour MP was excruciatingly, ridiculously awful. It may seem like sour grapes to say that, but it's simply a fact. I've felt all along that McKenzie was the weakest of the four main candidates, so depressingly there's more than a whiff of the old "monkey with a red rosette" syndrome about the result.