Today we got a glimpse of why the Conservatives are probably going to lose the next election

If the British economy starts to recover quite vigorously in 2013/14, the Conservatives will have a much better chance of holding on to power at the next election. Vigorous economic recovery looks unlikely, however. Things may well feel pretty flat for the foreseeable future.

But even in a flat (or worse) economy, if Labour fails to establish greater credibility on economic management, especially as far as cutting the fiscal deficit is concerned, election victory will remain out of reach. The famous (and clichéd) “jury”, aka the electorate, is still out on that one.

I mention these things to set a realistic context for the slightly more excitable words that will follow. Because in the final PMQs of the year I thought we got a glimpse of why the Conservatives are probably going to lose the next election.

The moment came during the exchange over food banks. Ed Miliband lobbed up an apparently gentle question about the greatly expanded demand for their services. If it was a trap it was skilfully camouflaged one. And perhaps the calmness of the questioning tempted Cameron into relaxing a little too much.

But, unwisely, Cameron did relax. Latching on to the concept of volunteering – prompted by Miliband’s mention of food bank volunteers – the prime minister claimed the “success” of food banks as an example of “what I call the Big Society”.

This was a hopeless response on a number of levels. First, it was a characteristic example of Cocky Cameron, trying to place himself at the centre of a story. Second, it was myopic, claiming that a sadly doomed political idea still had life in it. But third, it reminded us that there has turned out to be, to put it kindly, a bit of a gap between the image of sunny, compassionate Candidate Cameron and the reality of life under prime minister Cameron.

Itwas an open goal, and Miliband netted the rebound:

This was a moment that could inspire Labour’s attack on the government’s record between now and polling day. The Conservatives told us they had changed, Labour will be able to argue, but in office they looked more like an 80s tribute band, and a pretty talentless one at that. We were told that something marvellous called the big society was coming. But in practice this meant food banks springing up all over the country. Indeed, the prime minister himself claimed their growth as a sign that his big society vision was being realised. That is not a big society that anyone could want to see.

There is a long way to go to the next election. Over the next two years the unexpected will happen, as it always does. Labour’s poll lead is good but not yet good enough.

But, in this last session of the year, a potentially fatal crack opened up at the very centre of the government’s façade. We haven’t heard the last of this.