This is one of a series of essays that can be found in The State of Independence: Key challenges facing private schools today, edited by Jane Lunnon and David James and published by Routledge 

It is a lesser known fact that it was the middle classes that brought down the grammar school system.

This is a big statement, and one that’s hard to prove. But it is without doubt that many in the middle classes were, by the early 1970s, happy to wave goodbye to the 11-plus because they perceived - correctly - that their kids stood a good chance of failing and being sent to a secondary modern. They were no longer willing to roll the dice.

For their kids to be excluded from elite education and condemned to what was often second-class schooling meant that they were willing to accept what was memorably described by right-wing journalist Stephen Pollard as the “single greatest act of educational vandalism”: the abolition of grammar school education through most of the country.

In 1965, when Circular 10/65 was issued by the Labour government (when the education secretary Tony Crosland was reported by his wife to have vowed to “destroy every fucking grammar school in England”), there were more than 1,200 selective grammars - 15 years later there were fewer than 170.

Herein lies both a warning from history and a profound contemporary challenge to the independent sector: if the affluent middle classes - the readers of the Daily Mail and the Daily Telegraph - perceive that a public-school education may no longer be available to their children and grandchildren, then they will not hesitate to support a politician who promises educational corrective surgery.

The reason the middle classes might feel alienated or even excluded from independent education? A perception of rocketing school fees, of course, and the widespread idea that these schools are backfilling with rich kids from South East Asia and Russia.

Private schools have become a political football

So far, so well trammelled. But there is a further danger for the independent sector as yet not really explored: it is a lesson from the world of further education. What isn’t experienced by the political or media classes is likely to be ignored, undermined and killed by a thousand cuts. It is often observed that the reason the vocational college sector is treated so poorly by the government is because no cabinet minister or newspaper editor has ever sent their son or daughter to college. I would suggest that we are close to reaching the same situation for much of the independent school sector. Most MPs and journalists cannot afford the fees of a London day school or an HMC boarding school.

It is a truth near universally understood in this brutal political climate that what isn’t experienced personally, isn’t understood. And what isn’t understood can be used as a political football.

We are at that point.

Two years ago Michael Gove, a former (privately educated) education secretary who educates his kids in the state sector, used a Times column to ruthlessly kick the independent sector in a way that would have been unthinkable by a Conservative politician even a decade ago. And then Justine Greening, when education secretary, used a Green Paper to threaten private schools if they didn’t play ball with her agenda.

In short, the independent sector is losing (has lost?) the battle for hearts and minds among both the ruling classes and the aspirant middle classes. But I’m not sure many in the sector truly understand the extent of their predicament.

The political wind is changing - and not just amongst the Tories. Tony Blair’s New Labour was prepared to hold the indie sector close, even making it a cornerstone of its academies strategy - but a Jeremy Corbyn-led Labour is a very different proposition. What is more, even without winning an election, Corbyn is clearly changing the terms of the debate (by moving what is sometimes called the Overton Window) and making hitherto unthinkable policy ideas more mainstream. Abolition of independent education is openly discussed in Westminster.

Attend any contemporary gathering of independent schools and their heads, and representatives will explain away fee rises, insisting that it’s not just because of the gratuitous construction arms race but also a consequence of other costs rising, such as pension contributions. They will then go on - with a degree of inevitability - to discuss the enormous lengths that they are going to to increase bursaries (without mentioning that many of these bursaries will not be for the genuinely poor, but will instead go to subsidising the middle classes who can no longer afford their schools). In some, limited, cases, this twin-track approach might have some success in winning around critics, but for many it will be way too little, way too late. And that is before we even start discussing the challenge of improved results in many comprehensives.

The scale of the PR and political challenge faced by the independent sector is Leviathan. Something radical needs to be done to avert disaster.

Ed Dorrell is head of content at Tes

This is one of a series of essays that can be found in The State of Independence: Key challenges facing private schools today, edited by Jane Lunnon and David James and published by Routledge. It is available here