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David Cameron has argued that a Labour government dependent on SNP support would mean “total chaos”. All this scaremongering is really about trying to persuade voters in England and Wales to vote Conservative.

It is a very negative approach, but it might well work. In keeping with similar findings in other polls, a YouGov poll for last week’s Sunday Times found that when asked to think about the possibility of a Labour-SNP deal, 40 per cent thought that ‘Labour would do a deal with the SNP, and it puts me off them’. The equivalent figure rises to 50 per cent among Lib Dem voters and 58 per cent for those currently intending to vote Ukip.

Britain may be starting to experience what political scientists call ‘coalition-directed’ voting. This is common in countries where coalitions are the norm. It does not necessarily refer to coalitions (it could mean ‘confidence & supply’), but it is easier to refer to the group of parties that gets to control the government as a coalition.

The idea of coalition-directed voting is that you do not just vote for the party with the policies you like best. You take into account the chances of different potential coalitions and use your vote to try to influence which one wins.

Britain may be starting to experience what political scientists call ‘coalition-directed’ voting.

For example, in 2009 Christian Democrats in Germany were successfully encouraged to vote for the FDP so a centre-right coalition could replace the previous grand coalition. Somewhat conversely, in the 2007 Danish election the centrist New Alliance gained support from those who were concerned about the far right People’s Party gaining too much influence. There are many other cases.

The overall aim of coalition-directed voting is to influence government policy by voting not just for a party, but for a government.

So, on this basis, if Tory voters were really worried about the SNP’s influence, they should vote Lib Dem in competitive Tory-Lib Dem marginals. While this could lower the Tories’ number of seats, it would increase the chances that a Labour-led government does not depend on the SNP while also not much damaging their own chances of forming a government.

Tories might be anxious about undermining their own chances of winning an overall majority. But the chances of a Conservative overall majority currently look pretty small, and in any continuation of the Con-Lib coalition the Lib Dem contingent will still be much smaller than in 2010.

And Tory modernisers might like more Lib Dem influence. The Conservative right should weigh up the benefits of Lib Dems moderating Labour with the costs of Lib Dems moderating their own party.

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This kind of thinking also applies on the left. Labour and Green and even SNP supporters might want to vote Lib Dem to moderate a Conservative-led government and limit the chances of Ukip influence, even at the cost of their own MPs.

This, of course, is what the Lib Dems in effect argue when they warn of Ukip or the SNP holding the balance of power. And there is some evidence this is cutting through. A YouGov poll recently showed that 44 per cent of those currently intending to vote Labour agreed with the claim that a Con-Lib coalition would have more heart than a Tory majority government.

‘Coalition directed voting’ is what the Lib Dems in effect advocate.

Meanwhile, 46 per cent of those intending to vote Tory agreed that a Lab-Lib coalition “would have more brains than a Labour majority government”. Probably more would accept the idea that Lib Dems would make Tory government policy closer to that for Labour and vice versa. There seems to be plenty of Tory and Labour supporters who are open to the idea of ‘coalition-directed’ voting.

Strangely Nick Clegg undermined this powerful argument somewhat when he ruled out arrangements with either the SNP or Ukip last week. Given the very small number of seats Ukip are expected to win, there is only a small chance that they would be vital in providing a majority for a DUP and Lib Dem-backed Tory government.

But the chances that any Labour led government will need SNP support are large. So to rule out supporting Labour in these circumstances reduces the attraction of ‘coalition-directed’ voting: why would a Tory vote Lib Dem if Clegg won’t moderate the Scots?

Coalition-directed voting can also benefit parties on the extremes as well as centrist parties. Left wingers in Scotland might vote SNP to keep a Labour led government to the left. Eurosceptics anxious about immigration might want to support competitive UKIP candidates to influence a Tory led government.

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Ed Miliband and Jim Murphy have been fond of arguing that that there should not be any post-match analysis until after the voters have decided. But voters cannot make properly informed decisions without understanding who would do what deals with whom.

There needs to be more information and analysis about potential governing arrangements, not less. And it needs to be constructive: asking parties more about what they have in common and what they might achieve together than about ‘red lines’. The points of contention might be more exciting to discuss, but programmes for government are built around points of consensus.

If coalition-directed voting is not radical enough, a dramatic and still more effective strategy for the Tories would be to offer a grand coalition in the event that Labour might otherwise govern with SNP support. If the Tories are not prepared to do that, then how seriously concerned about the SNP are they?