My personal income is lower now than it was 20 years ago - in nominal as well as real terms. But I'm happier in my work and life now than I was then. Which poses the question: why do the main political parties regard the threat of stagnation with such fear? Why don't they accept that they have no great ways to materially increase long-run growth - this generally witless collection of proposals highlights the paucity of thinking - and think instead about ways to improve Mill's 'art of living'?

The answer, I suspect, is that governments need economic growth, for a mix of reasons:

1. Economic growth is necessary, if not perhaps sufficient, to reduce unemployment.

2. To overcome Baumol's cost disease. The relative cost of government services such as health and education tends to rise over time; this is not (just) because of public sector inefficiency - look at how private school fees have risen - but because of the nature of the beast. Without economic growth, this tendency would generate a rising tax burden and growing tax resistance.

3. To get out of a debt trap. Higher growth allows governments to run looser fiscal stances whilst stabilizing the debt-GDP ratio. It's an alternative to austerity or the embarrassment of monetizing the debt.

4. Economic growth can divert attention away from questions of equality and redistribution. If per capita GDP grows by 2.5% a year then in 25 years time we'll be 85% better off. This means that, ceteris paribus, the minimum wage will be ''450 a week - not far shy of the median wage today. The passage of time, then, relieves poverty. If, however, the economy stagnates then poverty relief becomes a zero-sum game; it requires actual redistribution.

5. In a normal growing economy, a government that promises economic growth can take the credit for what probably happens anyway, as a result of private sector decisions.

All of these reasons have something in common. They all suggest that economic growth is helpful in preserving the legitimacy of the state. Sustained mass unemployment can generate riots and crime or - remember the 30s - worse. The higher taxes that points 2, 3 and 4 suggest would accompany stagnation would lead others to suddenly discover their inner libertarian, and would intensify distributional conflicts. And the absence of growth would sharpen the question: what the heck is it that governments do for us anyway?

This is no idle pessimism. The decline of growth rates in the 1970s led to serious talk of a 'crisis of democracy' (pdf). Who's to rule out a repeat?

In this sense, I fear some greens under-estimate the trouble which and end of growth would cause.Maybe governments are right to fear stagnation. Which makes it all the more troubling that they can do so little to stop it.