If you care at all about the future of quality journalism, you really should read Peter Oborne’s letter resigning his post as Chief Political Commentator of the Daily Telegraph.

He doesn’t pull his punches, my favourite bit being where he recounts the sensitive, thoughtful response of the paper’s chief executive Murdoch MacLennan, when Oborne put it to him that the Telegraph had been taking its readers for granted.

Said MacLennan with the charm and insight for which he is justly renowned: “You don’t know what you are ****ing talking about.”

Oborne isn’t always right about stuff. I think his take on the Cameron administration, for example – that it’s radical and bold and brilliant and woefully underrated – is about as far from true as it’s possible to be. But when Oborne gets it right he gets it very, very right and that particular occasion was one of them.

Yes of course the Telegraph has been taking its readers for granted.

You only have to look at things like the picture caption the other day, where Winston Churchill’s wife was billed as “Lady Clemmie Churchill.”

But that’s not her name and it never was her name. Lady Churchill, yes. Lady Clemmie Churchill, no, because that would imply – incorrectly – that she was the daughter of a Duke, a Marquess or an Earl.

Perhaps in the Guardian such a solecism might be understandable. But the Telegraph, remember, has been for generations the house journal of the Tory shires, as represented by people like Oborne’s late grandfather.

My grandfather, Lt Col Tom Oborne DSO, had been a Telegraph reader. He was also a churchwarden and played a role in the Petersfield Conservative Association. He had a special rack on the breakfast table and would read the paper carefully over his bacon and eggs, devoting special attention to the leaders. I often thought about my grandfather when I wrote my Telegraph columns.

War hero, churchwarden, Tory stalwart: people like Oborne’s grandad were and still are, those that are left, the backbone of the nation and the guardians of our heritage. For them, details like the correct appellation for the wife of a knight or a lord matter. Which is one reason why, when I joined the Telegraph as a diarist in the late 1980s it was drummed into us from the start that we should avoid such solecisms on pain of death.

We learned, for example that the phrase “run amok” should only be used in the context of Malays. And that the proper term, in most instances, for the “Union Jack” was in fact the “Union flag.”

At the time, like most know-nothing whippersnappers with ideas above their station, I found this antediluvian obsession with arcane detail quaint to the point of silliness.

Now that I’m older and wiser and have seen what has happened to our country in the interim, I suddenly realise the point of all that sticklerish editing and subediting. It wasn’t just about correctness and exactitude, important though both those qualities are in all professional writing. Nor was it merely about pandering to the readers’ pedantry, important though that is too because the business of all business ought to be about making your customers happy. It was, ultimately, about an ideal of what Britain – and by extension, Western Civilisation – should be.

What the Telegraph recognised in its glory days is that regardless of how quickly the times were changing there was a certain basic corpus of knowledge that should remain immutable – and impervious to dumbing down. So, if you became a Telegraph reader, no matter what your class or educational background, you could be sure to be treated as a fully civilised, rounded, intelligent adult.

It’s quite possible that some aspirant readers wouldn’t have known at the beginning that deer “stalking” and deer “hunting” are two entirely different things. But they would pretty soon because in the old days, the Telegraph would never in a million years have failed to observe the distinction between the two. Not because they were country sports snobs – well, not just because of that – but because one is the British term for tracking down a deer with a rifle and the other is the term for chasing after a deer on horseback, and there’s an end to it: it’s a simple question of getting things right.

And I haven’t yet got on to Oborne’s other main accusation against the Telegraph – that, increasingly, it is allowing its editorial policy to be dictated by its advertisers. Yes, to a degree this has become accepted practice in the glossy magazine world. But never in the news sections of newspapers of record, which is why Oborne’s allegations that the Telegraph toned down its coverage of the HSBC scandal because HSBC is one of its most generous advertisers are so depressing. There was a time when the proud culture of the journalistic trade simply would not have countenanced such behaviour. If you can’t speak without fear or favour, what is the point of being a journalist? Speaking truth to power is about the job’s most important perk.

Perhaps things look different if you’re running the business side of a newspaper and you’re panicking about the growth of this newfangled digital world which you don’t quite understand and about the rapid decline in print sales and the terrifying possibility that you might not get your million pound bonus.

But from an old school journalist’s point of view, I’d say the Telegraph has made a terrible mistake in betraying its core audience, its heritage and its standards in the way it has done.

Just because this funny new interweb thing has arrived doesn’t mean that we should all suddenly check in our brains at the coat-desk and abandon everything that ever made the trade of journalism honest and worthwhile.

Nor does it mean, just because people are gravitating towards the web, that the old media is yet dead. A fair chunk of the Telegraph’s profits – indeed the vast bulk, I suspect – still comes from the advertising for the print editions bought by the kind of old-fashioned Telegraph readers for whom the Telegraph nowadays has such apparent contempt. Unlike a lot of online browsers they actually pay for the product. They deserve better than this.