Imagine – it's easy, if you try – a government that one day decides that most, if not all, New Zealanders should lose a bit of weight.

Imagine this future government decides it has a right, nay, a duty, to do something about this.

You can probably write the script yourself: ageing population, burden on the taxpayer, rising health costs, alarmist stories about the blubbery equivalent of the "grey tsunami", the impact on productivity of having a bunch of lard-arses in the workplace…

I know we can expect our hypothetical future government to dress this up in “sensitive” language, but this what it will all mean.

Citing all these things, plus weight limits on airlines and other public transport, wear and tear on pavements and the like, one can imagine this future government deciding that – for our own good, of course – that Something Must Be Done.

The SMBD Rule, we shall call this. It is one of the most evert-present rules of politics, and it is ever-present because the assumption is embedded, deep within our body politic, that politicians can fix the great bulk of life’s bad things, if only we give them enough power to do so.

So, then, we can see this future government deciding that, as most of us need to lose a bit of weight, we all shall do so, whether we want to or not.

There could be an initial goal of, say, 4kg a year. Most of us could stand to lose that much weight (my GP, if he is reading this, will be snorting "and the rest!" in my own case).

We can expect the country’s weight loss programmes – Jenny Craig’s, Weight Watchers, and the like – to be lobbying for the compulsory enrolment of all of us in their programmes, to lose a minimum of 4kg a year, for at least a few years.

These weight loss programmes will be doing so not out of any concern to drum up business – perish the thought – but because they are worried about the long-term impact of the country’s poor weight loss habits.

You can see, can’t you, where this is heading? The analogies are not perfect with the arguments for compulsory saving – there is no such thing as a perfect analogy – but there are sufficient similarities to give pause for thought.

The compulsory savings issue got another rise this week, when United Future leader and Revenue Minster Peter Dunne noted, in a speech to the finance sector, that he is in favour of such a move.

This was nothing new – Mr Dunne has been on the record as favouring compulsory savings for some years now – but Labour, which made compulsion a feature of its 2011 election campaign and is gearing up to make it the centrepiece of its 2014 programme, quickly put out a press release welcoming the announcement, with finance spokesman David Parker saying this leaves National largely isolated in opposing compulsion.

That is not quite right, of course: neither the Maori Party nor Act favour compulsion, and the Greens position, oddly enough, is closest to National – auto enrolment for everyone who has not yet joined, but with the ability to opt out.

The Greens though add to this a "public option" KiwiSaver account to be run by the Guardians of the New Zealand Superannuation Fund.

The party most in favour of compulsion is of course New Zealand First, whose leader Winston Peters has been campaigning for compulsory savings for a couple of decades now, although his stance has undergone some important shifts over time (the compulsory savings were once to replace the state pension, whereas now they are to be on top of the pension).

This though was perhaps the most important thing about Mr Parker’s comments – they show Labour moving to a firmer embrace of New Zealand First and further away from the Greens as a political ally.

The savings issue is going to be – barring some major disruptive event – the central issue of the 2014 election.

Compulsory savings has a certain gut attraction for a lot of people. Most of us know the country could, and should, save more.

The trouble though is it appears a bit, well, nanny-state-ish. It means a government which is already appropriating a third of our income is going to compound this by compelling us to put a bit extra aside, as though we were not able to do that ourselves.

The evidence of the past few years is that New Zealanders are in fact getting the message that they need to save more. It can be seen in the numbers not only joining KiwiSaver but also saving through other means; and in the low increases in debt levels, now running below nominal GDP (which means a decline in real terms).

This seems more than a short-term reaction to the latest economic jolt – previous downturns have not seen this sort of behaviour, and the new-found love of saving has being going long enough for even the more sceptical economists to start to assume this behaviour is a long-term shift and not just a short-term fright.

It is, as an aside, one reason why GDP has not picked anywhere near as much as economists were predicting – people are simply not spending as much, because they are saving and/or paying off debt.

Which means bossing us all into saving a portion of our income is probably a bit redundant.

Now: if a few more of us can just get to the gym a bit more often….