Initially, the question of leaders’ debates was all downsides for Team Cameron. A debate would give Miliband the privilege of equal footing with the Prime Minister, and offer Farage an opportunity to take potshots in the hope of a securing a Cleggmania-style moment.

As has been widely suggested, their calculation was that the pain of refusing to take part would be more bearable than the risks of agreeing. Thatcher, Major and Blair all refused for the same reasons in their day.

But the Downing Street response was cleverer than a simple “No”. They decided to hedge against the risks of eventually being compelled to get involved, by using the time spent refusing to create some downsides for Miliband, too.

The argument for including the Greens is a valid one, as we have repeatedly argued here on ConHome – they qualify on all sorts of measures for the same level of coverage as UKIP (or the Lib Dems). But it is also proving helpful to Cameron’s cause – even before a single debating podium has been erected, the free publicity for the Green Party drummed up by the row has eaten into Labour’s share of the polls.

The gruelling process of hanging tough has paid off better than Tory strategists could have expected – not only have the polls shifted somewhat as the Left splits, but the broadcasters have now suggested a 7-7-2 format. This would see the Conservative, Labour, Liberal Democrat, UKIP, Green, SNP and Plaid Cymru leaders all take part in the first two debates, followed by one Miliband/Cameron head-to-head.

This would be even more harmful to Labour’s prospects. Sure, Cameron will still be at risk from a Farage barrage from his right, but Miliband will be making the same arguments as at least three other competitors – Natalie Bennett, Nicola Sturgeon and Leanne Wood. The only way his space could be more squeezed would be if Russell Brand was allowed to take part. The Labour leader’s argument will be diluted, and three parties competing mainly for the Labour vote would have the opportunity to make some headway.

A debate would still be a huge risk for Cameron, but the addition of some downsides for his opponent certainly softens the blow a bit. Nor is the struggle over yet – the DUP are reportedly arguing that if the SNP and Plaid are allowed onto the stage, then they should appear, too, so it seems likely to drag on further.

As an aside, it’s also a glimpse of the peculiar dynamic of this election. The rise of minor parties and popular disillusionment with mainstream politics both threaten to make this an election which will be decided by which party loses least badly.

It’s a bit like the Cold War, when America and the USSR never exchanged blows directly but instead hoped the other would be sufficiently weakened by a third party – either the Tories will be sufficiently sapped by the UKIP Vietcong, or Labour will be laid low by the Green, SNP and Plaid mujahideen.

It isn’t a glamorous approach, and it made the Cold War a grim, protracted struggle – but for one side the strategy did eventually work.