There it was again; last week, yet another call to "phase out grammar schools." Researchers at Sheffield Hallam University and the National Centre for Social Research have found that grammar schools and faith schools are socially exclusive and draw the overwhelming majority of their pupils from wealthier homes. Specialist schools, which can select up to 10 per cent according to a particular aptitude, are doing so in ever greater numbers. They too are accused of being "socially selective by default", since more affluent families are better placed to fund resources, travel and opportunities for their children to develop skills in, say, music, languages or even sport. The National Union of Teachers’ Steve Sinnott was quick to capitalise on this, "nailing the lie that selection helps those from disadvantaged backgrounds. On the contrary, it widens the gap between the haves and have-nots."

Is that true, though? And should we worry about it? The answers have to be yes, and yes. Social mobility is declining in the UK. The most recent international comparison of school standards, the Organisation for Economic Co-Operation and Development’s (OECD) PISA study, demonstrated that the UK has the biggest gap in the world between the best performing schools and the worst. Of course we should be concerned. It's a national disgrace.

But what we should not do in response is to allow the self-proclaimed levellers to jump on the social divide bandwagon and demand the closure of the160 remaining grammar schools - let alone of the entire independent sector which usually gets tarred with the same brush at this stage in the argument. To regard this segment of schools, identified by the PISA report as the best in the world, as creating - indeed, being -the problem and thus seeing their abolition as the solution is crazy. To close the best schools in an attempt to improve the least successful is about as sensible as shooting the first 200 runners in the London Marathon to spare the feelings of the rest of the field. The survivors might feel better, but there is no evidence that they'll have improved their performance as a result.

There's the rub. The best bits of the system should surely be part of the solution: in the UK, however, they are characterised as the problem. The wreckers would like to get rid of the high-performing schools, but there's no reason to believe that all the rest will improve as a result. Yet there is a peculiarly British feeling that there's something a bit grubby about excelling.

Of course, as a nation we're terribly good at (and awfully brave about) losing, but losing well. The stiff upper lip is alive and flourishing. And grown men don't cry (except for the odd footballer). But there's something in our national psyche that equates excellence with elitism: not elitism in the original sense of identifying and celebrating the best, but in a new and contemporary interpretation with a dirty connotation of social exclusivity. This collection is wrongheaded, but it is both strong and prevalent in just the same way as any mention of independent education and media leads inevitably to the monicker "public schools" and the inclusion of that quaint old 1896 picture of two Eton boys in their school uniforms and top hats juxtaposed with two local urchins. A picture is worth a thousand words, particularly if it’s obsolete and misleading.

In my inaugural speech as HMC chairman last October, I described how I believe the politics of envy are alive and well. If anything, the intervening four months have seen envy blossom. What kind of country, ruing the gap between best and worst, would seek to destroy the best? Britain, apparently, or at least some parts of it. I recall, as a very inexperienced head in 1991, talking to my opposite number at one of the (then) prestigious new city technology colleges. "If Major loses the (1992) election," I asked, "Do you fear for your school under Labour?" My colleague was sanguine. "Do you think anyone would be daft enough to have a go at anything as good as this?"

Kevin (later Sir Kevin) Satchwell of Thomas Telford School was right then. Knowing him, he's probably right now. But his comprehensive school is hugely oversubscribed, and the admissions police are now out in force. Will he have to hold a lottery for places as other schools are starting to? Lotteries aren't fair: but they're equally, illogically unfair to all, which is a kind of rough justice.

The government has failed since 1997 to grasp the nettle of over-subscribed schools. It simply ducked the issue of selection. But if the best schools are so good because of selection - and they are - it's time politicians stopped pretending they aren't there, turning a blind eye, sanctimoniously concentrating solely on what they tend to call "the vast majority of schools" and choosing to ignore the danger to the country’s best schools. If selective and partially selective schools are failing to find talented children from poor homes then, rather than lambasting the schools which have to make those hard choices, we should be taking a hard look at the social policies that are failing to tackle poverty, disadvantage and lack of aspiration. Schools are not the villains here. They aren't conspiring to exclude children from less affluent homes: but government and society are in danger of doing so, acting out of a warped and damaging sense of misguided egalitarianism, one that drags down instead of raising up.

Independent schools are actively looking for talented, disadvantaged children - without government help but, mercifully, without interference either. Maybe the government should do the same for its own schools (and silly new targets for Gifted and Talented children won't do anything to help). Why not help selecting schools to continue to thrive, and then focus on building up the remainder? Not those in dire straits, many of which are already enjoying streams of new money through Academy status, but those bumping along in the middle. They are largely ignored by government which should be pouring resources, ideas, innovation and talent into them, instead of hedging them about with red tape and the constant threat of hostile inspection with the dubious justification of public accountability.

We won’t make struggling schools better by destroying those that are already flying. But that’s the proposal that is being aired too often, and without being countered sufficiently strongly. If we’re not careful, this country will begin to slip down the path that’s being charted by those negative voices claiming to speak for equality – voices which, instead of being greeted with outrage or simply laughed out of court, seem to be granted ever-increasing column inches. If we’re not careful we shall end up labelling all excellence or aspiration as elitism, destroy what is fine, good and truly world-class. If we allow that to happen, we might as well pull down the shutters and proclaim the end of UK plc.