Labour commentators worry about Miliband’s “35%” strategy and how he might reach out to new voters. Conservatives wonder why economic growth has not yet converted into more polling support, and Twitter is filled with petty debates about Michael Gove’s latest literary remarks.  But the electoral significance of all of these issues is dwarfed by the two great electoral imponderables: How much will Lib Dem support pick up compared with their current polling position; and how much will UKIP and Green support fall back?

The scale of the assumed movements in these variables – the Lib Dems perhaps rising 7% or more, UKIP falling back 6%, Green support virtually vanishing outside Brighton – is enormously greater than any plausible direct movement between Conservatives and Labour.

Obviously there are various polling analyses one can do to probe how likely some kind of “reversion to the norm” is in Lib Dem, UKIP and Green votes.  Some commentators follow Dan Hodges in assuming the Lib Dems are bound to score at least 15% and UKIP no more than 6% and that (although there are some current Conservative supporters that will vote Lib Dem and UKIP supporters that will vote Labour), as a rough rule of thumb adding any UKIP excess over 6% to the Conservatives and subtracting any Lib Dem deficit below 15% from Labour should give a fair indication of the final result.

Others are not so mechanistic, but do in general assume that the Lib Dems will gain some kind of “governing party” dividend on the day.  Yet what interests me about this is the following train of thought.  Some Lib Dems say they believe they will gain something from having been in government on the basis that the old “wasted vote” argument, in the form that says “Lib Dems aren’t going to be in government, so you waste your vote if you go for them”, will no longer apply.  And that may be right.  But why shouldn’t what’s sauce for the Lib Dem goose be sauce for the UKIP or Green gander?  Why doesn’t the fact that the Lib Dems have been in government mean that UKIP and Green voters that might previously, at a General Election, have gone for one of the two main parties since those were the only governing parties, instead stick with their true preferences?

I’m going to labour this point a little, since I’ve not come across anyone else making it and when I’ve tried to ask folk about it they usually misunderstand me completely.  I’m not referring to the fact that some Lib Dem voters in the past may have been “anti-main-parties” voters and so might now switch to UKIP or anything of that sort (even though that may be true as well).  I’m saying: If the argument is that because Lib Dems are in government that proves that a vote for the Lib Dems is not a wasted vote, why doesn’t it mean that a vote for a minor party in general is not a wasted vote?

In the Westminster village, we may think the answer to that is that if there is a hung Parliament there is a much greater chance that the Lib Dems will be in a governing coalition than there is for any other party. That may be true (I’m not sure that it is – e.g. I’m not convinced Plaid Cymru or the DUP could not be coalition partners to others), but it strikes me as irrelevant whether it’s actually true.  Surely what counts here is whether voters believe it to be true?  Why would someone who doesn’t follow all the intricate day to day shifts in politics think it implausible that a party like UKIP might be part of a governing coalition if it got 10% of the votes?  Might not that seem extremely plausible, especially if (as seems very likely) all the talk in the run-up to the election is of polls suggesting a hung parliament is nearly inevitable?

Indeed, might not it even be the case that, the better the Conservatives appear to be polling, the more plausible it starts to appear that even a handful of UKIP MPs could tip the balance?  Even quite a savvy voter, who is aware that the Conservatives were around 20 seats short in 2010 and is aware of how unlikely it is that UKIP could get 20 seats, might think it plausible that either UKIP could hold the balance of power if the Conservatives were on, say, 322 seats or (perhaps even more pertinently) that a few UKIP MPs might tip the balance on a vote to hold an EU referendum, offsetting the effects of a few Conservative rebels.  (Analogous thinking might mean that the Greens, likewise, hold on to more of their opinion poll ratings come election day – perhaps diminishing the switch back into the Lib Dems.)

One awkward possible consequence of this is that even if the economy starts to drive support quite strongly to the Conservatives, support might top out just a little short of a majority, because the closer the Conservatives appear to be to such a majority, the greater the license for Conservative-inclined UKIP supporters – those who might vote Conservative to keep Miliband out of No 10 – just to stay with Farage.

My last remark here is that some Conservatives and Lib Dems assume that, in addition to a stronger economy helping the governing parties over the next year, there will also be a swing back to the government as has often been seen in the final months before elections in the past.  But a very smart old friend of mine has questioned how robust this idea is in the presence of fixed-term parliaments.  He points out that in the past, an upswing in support for the government any time in the last thirteen months or so before an election would trigger the calling of an election – it was the upswing in support for the government that caused the election, not the election that caused the upswing in support for the government.  Over the next year there will (as always) be periods when the government is more popular and periods when it is less popular.  But (economic improvements aside), do we really have a good reason to think there might not, randomly, be a swing down in the couple of months before polling day?

We may soon see another aspect of just how stupid that fixed-term parliaments “reform” really was.