There was a lot of talk in 2005 (not least from David Cameron) about bringing back National Service. Not the old kind, in which sullen conscripts were dispatched to distant military hotspots, but a new version in which bands of school-leavers volunteer for community service - thereby encouraging "national cohesion".
You can see the appeal: in an age of environmental upheaval, economic uncertainty and global terror there are all too many useful tasks that a quasi-military corps might perform, at home or abroad. But there's a flaw in the idea: the assumption that those involved should be young. What we should be considering is National Service for senior citizens.
OK, it sounds silly. But hold the jokes about square-bashing with Zimmer frames and consider the logic.
First: a system involving school-leavers wouldn't work. The old National Service died out largely because the young - and their families - hated it: not because the experience itself was miserable, but because they resented the enforced interruption to lives that were just taking shape. Why would it be any more popular today?
Nor would it be desirable. Tomorrow's young Britons will have to support record quantities of pensioners - and must earn the wherewithal to do so against cut-throat competition from emerging nations with younger populations than ours. Our economy will need all the youthful innovation and energy it can get. Should we really discourage school-leavers from finding their way into the job market?
But the over-60s and those on course to become over-60s in the next couple of decades - are a different matter. Most of us face a perplexing future. On the one hand, we'll need to work until we're 70 or more in order to pay for our retirements. On the other, anyone much beyond 50 is usually considered too much of a dinosaur to be worth employing. So who will we work for?
The state needs to confront this problem. As more tax revenue is swallowed up by pensions, it will become harder to provide public services at the accustomed level. Meanwhile, growing numbers, left on the employment scrapheap, will demand not just pensions in the future but benefits in the meantime. It's hard to see where the money will come from. So how silly would it be for the state to try to claw something back in kind?
The idea seems absurd only if you assume that a new National Service would look like the old. It wouldn't. Fifty years ago, serving your country required brawn, not brain, so we conscripted from an appropriate age-group. Tomorrow's public challenges are less likely to involve physical action than intelligent logistical support for ad-hoc responses to various needs, including natural or unnatural disasters. Who would you rather have performing such work? Feckless teenagers? Or the kind of skilled, reliable, experienced workers whom we've all seen getting marginalised in workplaces because they're "getting a bit slow"?
I haven't worked out the details. Perhaps the traditional "730 days" would be an appropriate term of service. Maybe it could even be fixed so that a spell of National Service became a formal rite of passage through which the middle-aged unemployed could qualify themselves to claim the State pension; or, perhaps not.
But the core points remain: it makes economic sense to use the labour and skills of people you would otherwise be paying to stand idle; and society could benefit hugely from tapping a reservoir of expertise that will otherwise drain away uselessly.
Sometimes, no doubt, the course of duty might expose those involved to danger. All the more reason to recruit from our senior citizenry. I see neither logic nor decency in society's traditional assumption that it is OK to throw away the lives of our young men, whereas the elderly - who are approaching death anyway - should be cossetted. But I don't envisage physical risk - or even discomfort - playing a big part in this. The idea would be to use people's minds, not their bodies.
None the less, some would greet the postponement of their long-promised twilights on golf-course or cruise-ship with tantrums. Others would plead ill-health, some justifiably. But I suspect millions would do their bit uncomplainingly, while many would welcome the opportunity to make an active contribution to society at an age when they are currently made to feel superfluous. You have only to look at the mortality statistics for men aged between 65 and 67 to see the void that retiring from regular employment leaves in many lives. A period of structured service to the state could help fill this.
Yes, there would be family ties to consider, though perhaps less urgent ones than among the young. But it must be within the wit of the modern broadband state to devise a system in which most people could perform much of their service locally. In any case, two years - an eternity to an 18-year-old - pass all too quickly when you're in your sixties.
And for many senior citizens - who are generally more socially ghettoised than the young - being called up to do new work with new people would be a life-changing liberation. They could return to civvie street rejuvenated.
OK, so it still sounds a bit silly. Yet I have a feeling that, as the decades pass and the demographic landscape shifts, we'll be hearing more of this idea. And if you find yourself standing next to me on a parade square around 2025, I'll be pleased to remind you that you read it here first.