Politicking and point-scoring around the prospects of televised leaders’ debates have gone into overdrive. It’s safe to assume plenty is happening behind closed doors, but much of the process is played out in public. Cameron has hardened his stance that the Greens be included, while the other parties have threatened to empty-chair him.

Whether or not you think the Greens should be involved, the politics of the negotiations are fascinating. But why does it matter so much if this small party is invited or not?

Political space

Cameron claims including the Greens is an issue of “fairness”, but his real calculation is simple. The Greens are more of a threat to take votes from Labour (and some Lib Dems), while Ukip are most damaging to the Conservatives (at least when compared to how people voted in 2010).

With Ukip’s rise, the right could be more divided than the left for the first election in decades. This is based on an old-fashioned spatial theory of voting behaviour, but regardless of whether voters still think in terms of left and right, it remains true that Labour are most under threat from a Green surge.

To increase his chances, Cameron needs the Greens (both in the debates and in the election coverage more widely) to ensure Miliband is dragged to the left as much as he is dragged to the right by Farage. In the jargon, Cameron needs to pull Miliband away from the “median voter”.

There is a chance this is all moot: Bennett is an inexperienced speaker, and may fail to take full advantage even if included. However, both parties should remember “Cleggmania”, and be wary of minor parties successfully casting themselves as the outsider to an unpopular political establishment.

Poker face

Refusing to take part in any of the debates is an almighty gamble. Cameron risks being blamed by the public and the media if they don’t happen.

It also allows every other party leader to put pressure on him, as Miliband attempted to do in this week’s PMQs. Any time he, Clegg, or Farage are put on the spot in an interview they can simply bridge to the debates: “If the Prime Minister thinks this is such a good idea, why won’t he come on and defend them in a debate?”

Cameron also runs the risk of being empty-chaired. The BBC, often accused of left-wing bias, would probably bottle it, but I wouldn’t be so sure about ITV and Sky. It’s unlikely we’ll see an empty-chair on our screens, but Cameron’s error may have been to underestimate the broadcasters’ eagerness for these debates to happen. Their willingness to proceed regardless may force him into a U-turn. Either way, the chance of the debates being called off altogether seems very slim.

Chicken

Cameron is a shrewd politician. If the debates go ahead a U-turn is might not actually be such a bad thing. He could say that although he believes it is a totally unfair outcome, he has listened to the people, and has decided that the most important thing is for the debates to happen. The word “chicken” has been bandied around by both sides, and that’s what this negotiation is: a game of chicken. The leaders are speeding towards the election, but Cameron has an advantage: he knows he can survive the crash.

Alternatively, Cameron might get his way if broadcasters’ enthusiasm translates into negotiation. Having Cameron there is more important than the Green Party issue, so they may accommodate his demands. One compromise could be allowing Farage into the BBC’s currently three-way debate to reflect their new Major Party status, and inviting the Greens onto the ITV debate.

Thus, Cameron holds a strong hand. While it’s unlikely he can stop the debates happening at all, he might get the Greens in. If not, he can leave it until the last minute and U-turn if he needs to.

The PM is also banking on most of this passing the public by. Few people who follow these party political stories are swing voters. Most who notice it will see Cameron’s as a cynical move, but the key swing voters he needs to reach are those who will end up watching the debates, or reading the reaction the next day. The means to his preferred ends matter less, because most people don’t care about the process leading up to the debates.

Just like the election outcome itself, the final format of the debates is impossible to predict, but it seems very likely that they will happen in some form, and that Cameron will play some part. It’s Cameron’s gamble, but one that could easily pay off.

Charlie Cadywould is a researcher at the think tank Demos