Jackie Asheley argues in the Guardian that the way to beat Labour would be for the Conservatives and Liberal Democrats to form an electoral alliance - each stepping down in some constituencies to the benefit of the other.
It is a familiar theme. When the Conservatives were in power people used to advocate a similar pact between the Lib Dems and Labour. It never happened, and nor, I suspect, will this one.
The problem is that the electorate does not behave in the way you expect. If a constituency does not have a Conservative candidate 50% of those who would have voted Conservative will stay at home. Of the rest, a fair slice will vote for a protest party, probably UKIP. Some will transfer to the LibDems, but a few will transfer to Labour, correctly regarding the LibDems as being more left wing on some issues.
Where a LibDem steps down the situation is likely to be even more confused, with Labour and Conservatives perhaps picking up similar numbers of votes - even if the LibDem leadership specifically recommends a Conservative vote.
To make matters worse, there are only a handful of constituencies where a pact could possibly be effective. Limit your analysis to England as voters have other choices in Scotland and Wales. Then, rule out any constituency where Labour has more than 40% of the vote. With the lowered turnout this vote is likely to rise close 50%. Rule out any constituency where the third place candidate has less than 10% of the vote. With abstentions and wild card voters, this is likely to produce a net gain for the second party of around 1%.
The problem is that if the third placed party has much more than 20% of the vote, it is starting to look like a three way marginal, where neither party will step aside.
In most of the constituencies where there is real potential many of the voters who could be won over in this way have already started voting tactically. The rest are the ones who will refuse to play ball.
Such a deal, if it could be negotiated, would benefit the LibDems more than the Conservatives. Conservative voters are more likely to turn out, even if their party is not on the ballot, and more likely to cast an anti-Labour vote. So the Conservatives should insist that the LibDems stand down in twice as many seats to make it fair. But the LibDems are very unlikely to agree to this.
Such pacts are more interesting to journalists than to parties.