"I think the biggest threat to our chances now is …" I eagerly awaited the conclusion to this sentence uttered in a conversation earlier this week with a senior figure in the Labour Party. This is someone who, not surprisingly given the coalition’s travails, is very upbeat about Ed Miliband’s chances of becoming Prime Minister. (He referred to "when" rather than "if" it happens, which is a new development in the tone around the shadow cabinet.)
So what would that threat be? Ongoing doubts about the party’s fiscal credibility? Lack of a clear narrative on what to do with public services? A divisive row with the Unions over how reconciled the party should be with the cuts it will inherit?
"… Boris," he said. This surprised me. I’m a bit of a Boris-sceptic, thinking much of the cheerleading on his behlaf is an expression of Tory frustration with Cameron , rather than a serious movement to get the London Mayor promoted to the job of Prime Minister any time soon. But the case was persuasively made. Everything that is now being said about his unsuitability for the top job and the unlikelihood of it actually happening was once said about his chances of being London mayor. He is, I was told, a real star who has managed his career well and, crucially, who animates people who don't usually care about politics. That is the Holy Grail in Westminster these days. The fact that he isn’t in parliament now and has another job? A minor hurdle, apparently. Once Tory MPs are convinced enough that Cameron is leading them to defeat their famously regicidal tempers will be fired and a way will be found.
I’m still not entirely persuaded but it is certainly revealing that Labour people are taking the prospect very seriously indeed. (My colleague George points out  that Jacqui Smith, former Labour Home Secretary, has intervened in a fairly vigorous attempt to debunk the myth of Boris bonhomie.) It wasn’t that long ago that Labour people were actually rather enjoying Johnson’s not so secret campaign to undermine Cameron and Osborne. They may have hated the way he kept Labour out of City Hall but the prevailing feeling was that his function on the national stage was as a convenient thorn in the PM’s side - an enemy’s enemy and therefore kind of a friend. No longer.
I was reminded also of a conversation I had a while ago with one of Ed Miliband’s advisers about the issue of charisma and personal ratings, where Cameron still beats the Labour leader in opinion polls. Wouldn’t a presidential-style contest between the two men be a problem for Ed? The answer: that is the received wisdom, yes. But consider how much of a hit Cameron’s personal brand has already taken, how limited his power is in coalition, how much some his own MPs dislike him, how jaded his act will seem by 2015. Is it so hard to think that, by the next election, a presidential face-off would be something Miliband might even relish? I was deeply sceptical of that proposition at the time and most people I have shared it with (including pollsters) have looked puzzled or snorted in disbelief.
But to hear Tories talk about their own leader is a masterclass in disillusionment and pessimism. Sometimes they seem to do a better job of talking up Miliband’s chances than their Labour counterparts. Partly that is because Labour MPs are desperate not to sound complacent and because they have more of an insight into how brittle and unready the party machine is when it comes to the prospect of fighting an election. The Tories know their own weaknesses on that front too, of course.
The Labour high command certainly isn’t writing Cameron off. Far from it. The feeling I get from talking to Miliband’s closest aides is that they know Cameron still outpolls his party and remains a formidable politician - "clearly he is still their strongest asset" – says one. The Tories, goes this view, would be crazy to change leader before the election. That remains a very remote possibility in any case. But something has definitely changed in the way Labour views their main opponent. There is now someone in the wings they would want to take on even less.