The Oldham and Saddleworth by-election is intersting for all sorts of reasons: the first since the general election; the first where two Coalition parties have fought each other (or not); the first sitting MP to be expelled by an Election Court for lying about an opponent (and let’s hope that doesn’t catch on or we’ll have no MPs left); and so on.

By-election results are most usually analysed by commentators in terms of “share of the vote” because they usually attract far fewer voters than a General Election – and indeed turnout was down from 61% to 48.6% since last May. But, and here the election is unusual, the fall in the vote is entirely accounted for by the fall in the votes of the two Coalition parties.

Labour increased its actual vote slightly – from 14, 186 to 14,718.

The “others” also increased – from 4,478 to 4,571.

It was the combined Tory and Lib Dem vote that dropped – from  from 25,856 to 15,641 – a loss of 10,215 votes or 39.5%. In other words, the entire drop in turn-out is less than the collapse in the Coalition vote.

Some commentators today are suggesting that if the Coalition parties had stood a single candidate they would have beaten Labour – which is mathematically true. They would, if their votes had combined, have had a majority of 923, which sounds good until you realise that their combined majority in May 2009 would have been 11,670! And of course this assumes all of yesterday’s Lib Dem and Tory voters would have voted for a Coalition candidate, which is not at all clear.

So O&S was in many ways a good traditional collapse of the Government party (or parties) vote – only normally it takes a bit longer than 8 months into a government for that to happen. So if I was in the Coalition I’d be afraid, very afraid.