John Rentoul: Not a great speech, but still effective enough to leave the PM in a quandary

The trouble with not doing spin is that it is itself a form of spin. When David Cameron's people tell us he woke up yesterday and decided to do away with the written speech, we do not say to ourselves, "Here is a man who is speaking to us from the heart". We say, "Here is a man who wants us to think he is speaking from the heart".

We wonder, was the speech really that bad, or did he always plan to speak without a text or an autocue? It is after all an obvious device, a way of acting out the Creation Myth of Cameronianism – the myth that, two years ago, in a single, brilliant, ad lib performance on this same stage in Blackpool he came from nowhere to seize the leadership of the Conservative Party from under the nose of the overwhelming favourite.

So now, after Tony Blair, the hated sultan of spin, we now have two competing forms of non-spin. The boring-is-the-new-interesting juggernaut of Gordon Brown, and the I'm-not-acting, I'm-not-reading-from-a-script David Cameron. Yet it is still spin. The scripts are in their heads, learnt by heart. From Brown, the day before yesterday in Iraq, saying that 1,000 troops would be home from Iraq by the end of the year, "indeed by Christmas". To Cameron yesterday, "it might be a bit messy but it will be me".

It was certainly a new experience for many journalists, accustomed to having a text handed to them by self-important press officers just before the leader strides vigorously on to the platform.

Normally, you can hear the rustle from the media section whenever the speaker comes to the end of a page. The last time we had to make notes was in 1994, when the final page of Blair's speech announcing the rewriting of Clause IV of the party's constitution was left off the copies handed out to the media. They were worried someone might tip off the delegates and there might be booing.

As a result, journalists had to pay closer attention to what Cameron was saying, instead of listening with half an ear while they scanned ahead in the text for the next interesting bit. And as a result of that the instant verdict was possibly more favourable than it would have been otherwise. Because, although the delivery was of high quality – he does "conversational" as well as Blair without then going into rhetorical overkill – the content was thin.

It was not just that it was familiar to anyone who had been paying attention to his many recent speeches – most of the audience in the hall or on television will not have been. It was that it was difficult to identify in what ways the country might be different under a Conservative government. The only one that stuck in my mind was that soldiers would have their leave calculated from the moment they arrive back in Britain rather than from when they leave Bagram air base.

The only insight offered by Cameron's speaking from the having-learned-by heart was in the quality of his mistakes. If you mis-read off an autocue, it might tell us about the poor sentence structure of that part of the speech. If you mis-speak off the cuff, it tells us what is going on inside the speaker's head.

And Cameron fluffed in the middle of his section, lifted from recent leading articles in The Independent on Sunday, about how Labour had broken the Military Covenant between the nation and its soldiers. He spoke of the "three battalions that should never have been abolished by the last – by this Government". It is not just bravado, then. He really does think Brown can be beaten in a general election which, as he went on to say later, could be "in one month or one year".

His speech, however, did not do the one thing to which all the pre-publicity had built up: it did not change the calculations about when that election will be. It did not bomb and thus tempt Brown to press the button. It was not a belter that forced the Prime Minister to hold off. Next week's decision is still finely poised.

This is surprising, not least to me. I said in print recently that Brown should go for an early election because things can only get worse and Cameron is a more formidable opponent than many Labourites think. George Osborne's assault on the tax loophole of non-domiciles is surely proof of that. But I also said that Brown would not go for an early election because of the danger – even if small – of being the shortest-serving Prime Minister since 1827.

I thought the Prime Minister was trying to close down the speculation on the morning of his speech in Bournemouth last week, when he told the Today programme that he did not need a new mandate to do the things he wanted to do.

But Mr Brown is a cautious politician, and, paradoxically, that has led him to recklessness, because he did not want to rule out the possibility. And keeping the possibility open has meant bringing forward the NHS review, the Comprehensive Spending Review and the pre-Budget Report, which only increases the "Grand Old Duke of York" cost of backing off now.

Wise heads in Blair's old entourage are shaking their heads, wondering how someone supposedly so good at seeing four moves ahead in the game of political chess could have got himself trapped in this way. One said to me this week that it was not the "process" issues that were the problem. "Why have you bottled out of an election?" is a story that will run for only a few days. So, equally, is the story, "Why are we having an election now?"

The problems for Brown are those of substance. If he does call an election next week, what is it about? What are the pressing challenges requiring difficult decisions that were not in the 2005 manifesto?

In the longer run, an early election, even assuming Labour wins by a reasonable margin – and a majority of 66 is harder to obtain because of boundary changes – could hasten the decay of Brown's authority. The moment the election is over, the question moves on to: "Are you going to fight the next one? Who will be the next leader, Ed Balls or David Miliband?"

And postponing the election, after allowing speculation to run away, also has a longer-term cost. The speculation will start up again, probably just before Christmas when political journalists have little to write about. Will there be a February election? Or March? Where the last days of Blair were dogged by speculation about the date of his departure, the next phase of the Brown premiership is going to be coloured by speculation about a different date.

David Cameron's so-so speech leaves Gordon Brown just where the Conservative Party wants him: between a rock and hard place.

j.rentoul@independent.co.uk

The writer is chief political commentator for The Independent on Sunday