Lately I've discovered there's a nice swimming pool within walking distance of my house, so I've been going there regularly. As I hadn't been swimming for a couple of years, the first time I tried it my muscles screamed at me, but the gist of their complaint was Why haven't you been doing this for so long? rather than Stop this at once!; I enjoyed it, staggered home, returned the next day, staggered home, and a week later I found myself illustrating a conversational point by dancing at two in the morning. It is most enjoyable to have energy.

It took me years to work out that exercise wasn't a punishment, and I blame school. This concerns me: Britain, as they keep telling us, has the highest rate of child obesity in Europe, so exercise, you unfit little tykes, is the current theme tune. But I remember sports at school. They made me determined never to exercise again in my life. And unless PE teachers are better now than they were then, I fear our nation's youth is not going to be very motivated.

The basic problem, in retrospect, is that people who become sports teachers were good at sports in school. Like most things, sports are easier to understand if you've experienced them yourself, and what sports teachers generally haven't experienced is the exhausted, breathless humiliation of trying to keep up in a marathon, the struggle to keep afloat in a swimming pool, the sheer maddening boredom of a half-hour of tennis where you know perfectly well that no rally is going to last more than five seconds because you are always going to miss the ball. Which means that PE teachers have no idea how to teach kids who are bad at PE.

Also, of course, they have less motivation to improve the entire class than any other kind of teacher. If your GCSE history class has a ten per cent pass rate, the head is going to have words with you, but if only ten per cent of your rugby class is good at rugby, then hey, that's your rugby team picked out for you, and to avoid trouble, all you have to do is stop the other ninety per cent from setting anything on fire for the duration of the lesson. PE teachers aren't held up to the same standards as academic teachers, and they aren't expected to ensure that everyone in the class is getting a reasonable education. The result is predictable: a ruthless meritocracy that focuses entirely on the kids who are already good, and ignores the ones who aren't.

It's hard to understand that someone else might find difficult something you find easy, and here's one thing I remember very clearly from school sports: no teacher ever showed praise or concern for the kids who weren't doing well. Put simply, they weren't able or weren't interested in distinguishing struggling from slacking. I still remember the helpless fury of outraged logic I felt as I thrashed leaden legs in the swimming pool, feeling about three lungfuls away from drowning, and heard a teacher yell at me, 'Come on, the more tired you are the harder you should kick!' It just didn't make sense: it was like saying 'The more bankrupt you are the more money you should spend!' Obviously the teacher had noticed I was slowing down, but a more encouraging phrase - 'Come on, you can make it,' or even 'Are you all right?' - was out of the question. PE teachers, at least all the ones I knew, are alarmingly inclined to assume a child that slows down is stubbornly idling rather than genuinely running out of energy, and shouting commands to someone to do something physically impossible only wears them down further.

There are several bad effects this has on unathletic kids, and they are profound. The first one is that the rich get richer and the poor get poorer: unathletic kids get almost no exercise during lacrosse or netball classes. Why? Because they quickly learn that a position where the ball will come their way is going to lead to embarrassing failure; instead, they get skilled at identifying and volunteering for positions that ensure the ball won't come their way. The concept of deep field is a familiar one to anyone who's ever been bad at sports, that blessed position where you may have to show willing if the ball ever actually does go off at an extreme angle and fly fifty feet, but otherwise you're quietly removed from the game, safe from humiliation. So instead of actually getting any exercise, the worse sportsmen of the class spend their cricket lesson standing in a field daydreaming, probably getting less exercise on the field than they got walking to and from class.

The second one is more insidious, and can have a permanent effect on the kid's later life. Badly-taught sports classes, particularly ones that are competitive (which, let's face it, is practically all of them), damage physical self-esteem in a way that it's hard for the average sports teacher to imagine. There's a very simple reason for this: as long as the teachers are concentrating on the kids that interest them, every time you have to run a lap or swim a length, the leaders set the pace. A couple of whippets zoom off, and everybody else dashes after them, trying frantically to keep up. Now, some people can just run faster than others; that's a fact of life. If you run at your natural speed, you can keep going for a very long time. If you're trying to run at twice your natural speed, you'll collapse very quickly. And if twice your natural speed is the pace you're trying to achieve, you're going to learn a poisonous lesson: your body is useless. It's incapable of doing what it's supposed to, it hurts even to try, and your failure will be conspicuous, because practically everybody you know will witness it.

Under such circumstances, is it any wonder that kids start to give up? Once they're convinced that their bodies don't work, they won't try to improve them; what's the point? And hey presto, what you have is a child for whom exercise is anathema, something they can't do.

Obviously that entails damage to their future health, because it'll make them far less likely to take exercise once they leave school, but, less visibly but just as importantly, it causes serious damage to their sexual self-esteem. Sex is a physical activity, and how can you engage in it if your body is useless? 'Useless' quickly translates into 'worthless' in an adolescent mind. Exercise can have a profound effect on how attractive you feel, regardless of how it affects how you look; a few days after taking up swimming again, having changed pretty much nothing about my overall appearance, I found myself bopping down the street feeling about ten times as attractive as I'd felt the previous week, just because my body felt healthy and active. It takes more than a couple of bad experiences to damage that, of course, and kids get more: they get publicly humiliated about the uselessness of their physicality between two and four times a week, every week, for over a decade, at a time in their lives when their self-esteem is forming. I don't think I'm misremembering this: the girls in my school who were bad at sport tended also to be the ones who shied away from flirtatious behaviour, pretty clothes, carefully-groomed hair and a general attempt to present themselves as attractively as possible. They went for the inconspicuous look, because whenever anyone in authority ever told them anything about their bodies, it was 'you're doing it all wrong'. PE taught them that being seen meant being criticised: the best they could hope for, in PE and in general, was not to be noticed at all.

The thing is, it doesn't have to be this way. Let me tell you a story. I was, all the way through school, a permanent and perpetual deep-fielder. My liking for sports was directly proportional to how much running they involved. My favourite was netball: although I still went for defense positions because I couldn't aim, the netball court, bless it, has ruled-off areas where you are and aren't allowed to go, which meant never running more than a few metres. Parental notes the minute I was even slightly ill, standing around, hiding at the back, I was accomplished at all of them.

Then, at twenty-two, I joined a gym, mostly to keep some friends company. The instructor put me on a running machine to show me how to work it, and, remarkably, it ran at a slow, steady pace - which is to say, a pace I could maintain. Utterly convinced I was going to collapse within thirty seconds, because that was what had happened every single time in my life I'd ever tried to run, I ran for a minute, then another, then another, then another, and I felt fine. It's impossible to convey the overjoyed disbelief I felt as I jogged and jogged: I was running, and it was working, and I wasn't going to collapse. It was a miracle.

The gym got too expensive, but did the lesson that instructor taught me stick? Let me put it this way: for several years, before I injured my knee and had to stop, I went jogging every morning, on my own, first thing, five or six times a week. Just because I felt like it. I had running shoes, I had a special CD-player belt, and a watch with a stopwatch feature that I only wore to run; I was into it. Once I played a game of tag with my friends, and everyone gave up on catching me because all the practice meant that I was too fast. I knew things I just hadn't known as a child: that if you find a pace that's comfortable to you, you can sustain it for a long time; that the moment two minutes in where you think you're going to die lasts about thirty seconds and if you plough through it you'll feel all right again; that fatigue increases rapidly when you begin and then the increase slows down, so you can just keep going and it won't get much worse.

In five minutes, that instructor had taught me how to use my body in a way that no one taught me in eleven years of schooling.

What I believe is this: school PE teachers have got to learn from gym instructors. The fact that they have bigger classes is not a good enough reason not to do this; once you've helped someone find their own pace, they can carry on on their own forever, and all you need do is keep a general eye on them. The first few classes of a new year, let most of the kids play around and one by one go through the class until you've got everyone finding a comfortable rhythm, and by the second term, you hardly have to monitor them at all. You can just put them on the track or in the pool and let them get on with it.

The essential component in this, which I suspect many schools would resist, is a drastic rearrangement of priorities, with the major casualty being competitive games. Instead, have everyone running laps at their own pace, or swimming lengths: what would actually get fitter children is PE classes that fundamentally resemble adult work-out sessions. I can't think of a good objection to this. It's supposed to foster team spirit, but does it heck: the kids standing in deep field are doing their best to contribute as little as possible, because they know they have nothing to contribute, and that their inevitable failures will annoy everybody if they even try; meanwhile, relentless favouritism is going on at the top end. Tell me how that fosters a we're-all-in-this-together camaraderie. It may be easier to monitor a whole class if they're in two teams, but if a third of the class are just standing around, the teachers aren't doing the job they've paid for, and anyway you can monitor a work-out just as well once you've helped everyone find a pace. It may benefit the school football team if the players can practice during class, but the football team is an extracurricular activity and should not be allowed to cut into non-members' class time. If you aren't allowed to play computer games during IT classes, why should you be allowed to play sporting games during PE? The school play may raise the school's profile, but nobody allows it to be rehearsed during English class while the non-cast members sit on their hands. Extend the analogy to any other class, and you'll see how profoundly iniquitous it is. School teams are extracurricular, and if kids love them enough to make them a worthwhile experience, they'll practice on their own time; they are not something that should be allowed to waste the time of other children.

I say this, incidentally, as someone who didn't go to a school that worshipped athletics. My school was competitive and high-achieving, but its main emphasis was on the liberal arts, with the most visible extracurricular stuff being drama and music. You got standing if you were in the school plays, and we had a lot of good orchestras and choirs, but while the lacrosse or fencing team occasionally related their adventures during assembly, if you told anyone 'Hey, the lacrosse team won the match against School X last night!', the usual response would either be, 'Oh, was there a match?', or, occasionally, 'We have a lacrosse team?'. Being on the sports team carried about as much cachet as being able to wiggle your ears: cool if you could do it, but really your own business. For people whose schools do make a big deal of the Team, where physical self-esteem gets mixed in with social self-esteem as well, it can only be worse.

If any Cabinet Ministers are reading this blog: here, take my suggestion. You can have it; you don't even have to credit me. Save the country! If, more probably, any sports teachers are reading this: try being nice to the unsporty kids. They're probably capable of more than you think, if you let them work up to it slowly. But do it gently, because here's the other thing: they probably hate and fear you. You cause them physical pain and humiliate them several times a week, and however innocently you're doing it, it'll make it hard for them to believe you have their best interests at heart. Would you like someone who did that to you? And if you're an ex-sportophobic, take my word for it: you can do more than you think. Start jogging at the slowest speed you can manage without it being a walk, or swimming at the slowest speed you can sustain without sinking. You'll be amazed at how long you can keep doing it, and how quickly you get faster.