Can the three interchangeable presenters rise to the challenge and get under the skin of three almost interchangeable leaders?

As one of nature's enthusiasts, a kind of Candide of the political scene, it is a struggle to be sceptical, let alone cynical. But as I listen to the excited outpourings of the broadcast political correspondents, I am left repeating the timeless cliche: "Well they would say that, wouldn't they?"

One live TV debate between the three main party leaders (tough luck, SNP) is certainly a political event. Three – well, that's the world of broadcasting diversity. But exciting? Well, maybe only to broadcasters. The politicians have finally recognised there is a forum for debate outside the House of Commons, and it's theirs.

Those commenting on this story are generally as sceptical as I am, fearing it will be all about sweaty upper lips rather than political ambition and fundamental beliefs.

I suspect that very swiftly the debate will be not Brown/Cameron/Clegg but Stewart/Boulton/Dimbleby. And, in a curious way, it should be. If this is to be a real, substantive debate where the party leaders are forced to confront the implications of their rhetoric, then it is the three presenters, ITV's Alastair Stewart, Sky's Adam Boulton and the BBC's David Dimbleby that will have to make them do it.

Tory bloggers wonder why David Cameron has exposed his poll lead to such a challenge. But if the debate chairmen (and heavens, how much more similar can you get that these three: white, top of the range, 50+ political personalities, brought up in the same school of political broadcasting. It's not a bad school, but others are available) can actually pin the players down, and – most centrally – get, for example, Cameron to address what he thinks the state can and can't do, and whether he really thinks what he has implied in speeches to his party conference and in the Hugo Young lecture, that the bankers are somehow less culpable than government in the current crisis. And get Brown to explain just why he so powerfully endorsed noble ends such as ending child poverty or feeding Africa, while creating the economic conditions that would make it most difficult to achieve them. And get Clegg to set out where his bottom line really lies. In short, if one of them can get the politicians to reveal their thinking – then there really will have been an advance for democracy.

But three interchangeable presenters will almost certainly just underline that our voting options in the election will be between three almost interchangeable politicians.

Yet a good debate really can change minds, or at least explain people's prejudices to themselves. I fear my mastermind-level knowledge of Barbara Castle's life is about to impose itself. But it was a debate on Europe that found her out. It took place at the Oxford Union in 1975, televised because no one would participate in a formal studio debate (aren't the political classes wearisomely slow to think about things in a new way?). And this was probably a decisive moment in the public perception of the campaign.

The Liberal leader Jeremy Thorpe – speaking with Edward Heath for the "yes" campaign – challenged her to resign from Harold Wilson's Labour government if the vote went against her. Her attempt to present her campaign as the last moment to defend Britain's ability to make its own laws was shredded by Thorpe's taunt. Surely, was the underlying message, if Britain in Europe meant its government became powerless, there would be no point in belonging to it. My country would need me more than ever, she retorted. Not a bad response really, but too many people already saw Castle as a self-promoting doctrinaire politician of the left. It was an invitation to derision, a confirmation of all that her detractors claimed about her, and about the campaign of which she was a leading member. It was not about principle, just party position.

What would be the killer question now? Or are Cameron and Brown locked in a kind of political waltz so closely choreographed that neither will allow the other space to reveal their true political selves, least of all in a debate chaired by interchangeable presenters?