Bullies are always cowards, they say – so it’s no surprise David Cameron is turning tail on head-to-head election debates between the only two candidates for prime minister. First he said the Greens must join – it was agreed. Then he said there must be seven parties – agreed too. Then it had to be before the campaign proper begins – agreed again. Ed Miliband yesterday gave the Martini challenge: he’d debate him “any time, any place, anywhere.”

Cameron’s people this morning resorted to lying, pretending Labour wouldn’t debate with the SNP. Never true – “utter nonsense” says Labour. As one excuse after another falls apart, Cameron’s spinners scapegoat the broadcasters, as if they were to blame for what they call “chaos”. The broadcasters have proved flexible – and everyone but Cameron thought the 7-7-2 format fair. There was nothing “shambolic” except Cameron ducking and diving, weaseling and wriggling. He will agree to just one debate with seven parties, knowing each question will get such a short time that he can dodge interrogation on any of the myriad U-turns, blunders, cruelties and dishonesties of his leadership. By going early, before his manifesto is out, it comes under no scrutiny.

Come hell or high water, Cameron dare not debate head-to-head with Ed Miliband – which is very odd indeed. Since their entire campaign is predicated on painting the Labour leader as weak, weak, weak, too incompetent to occupy No 10, why is he too afraid to confront him in public?

The broadcasters, constrained by impartiality laws, are unlikely to complain about Cameron’s obstructionism

Cameron’s red-faced bully-boy technique is a familiar spectacle as he refuses to answer any questions at PMQs but blusters and bludgeons back instead; Flashman on good days, an aggressive pub boor on bad days. But that style won’t work in answering questions from the public in a measured TV debate, which suits Miliband’s quieter style much better. Miliband’s personal ratings are so low that a moderately acceptable performance would be enough to dispel for many voters the idea that he would be unthinkable as PM. He would certainly emerge far better than expected to the many voters who have never heard more than a clip of him, nor seen more than the universally hideous photos in the rightwing papers.

The shameless Tory press today lined up to back Cameron, though surely their readers want the debates to happen. The broadcasters should stand firm and empty-chair Cameron, giving Miliband a town hall-style meeting – though standing alone has grave risks too.

But the broadcasters, constrained by impartiality laws, are unlikely to dare raise a hue and cry against Cameron’s obstructionism. If there is no great public outcry against Cameron’s cowardice, it will show, yet again, how far the political agenda this election is dominated by Murdoch, Rothermere and the Barclay brothers, who control 85% of newspaper readership, moving heaven and earth to keep the Tories in power. The Guardian/Telegraph offer of an online debate still stands – though the cringing Telegraph editorial today says “we welcome Cameron’s last-and-final ultimatum”. The Sun says: “David Cameron’s solution is right.” They have that on a repeat key for the entire election.

Nick Clegg’s caricature of Cameron’s position this morning was apt: “It’s as if they think they are ordering a drink in the drawing room of Downton Abbey and telling everybody else what they should do. It’s not for one party to grandly tell everybody else what’s going to happen.” Paddy Ashdown on the Today programme pointed out that Margaret Thatcher would never have run from the fight. But Labour reminds us that she was frit too when challenged to debate by both James Callaghan and Neil Kinnock.

The Lynton Crosby calculation is that chicken, frit and hiding behind the sofa insults will do less damage to Cameron than a straight one-to-one debate in front of the cameras. But they will find that whenever they try to run the “weak” Ed line, Labour will have a caustic comeback – if Ed’s so weak, why is Cameron so afraid?