Well-placed sources with inside knowledge of the Telegraph have said Peter Oborne's account of commercial pressure undermining the paper's editorial integrity rings true.

And Press Gazette has been told of pressure over stories about all of the big-four UK high street banks as well as major supermarkets.

Oborne, the title’s chief political commentator, has resigned from the paper on what he says is a point of principle. He suggested The Daily Telegraph’s scant coverage of the “HSBC files” was prompted by fears the bank would halt advertising, as it apparently has done in the past.

The Telegraph has denied the allegations and condemned Oborne for his “astonishing and unfounded attack, full of inaccuracy and innuendo”. A spokesman for the paper said "we utterly refute" Oborne's allegations, although it has not yet offered evidence which would disprove what he is saying.

Well-placed sources, who asked not to be named, have told Press Gazette that Oborne was “spot on”, and further claims have been made that:

The commercial department is “stronger” than editorial and that the set-up has been the Telegraph’s “dirty little secret for some time”

HSBC pays the Telegraph around £3.5m for advertising per year and is the worst organisation for seeking to influence editorial coverage

HSBC pulled advertising from the paper three years ago after revelations on accounts held with the bank in Jersey and that this represented a “watershed” moment for the relationship between editorial and commercial

Proprietor Aidan Barclay and chief executive Murdoch MacLennan are believed to have close relationships with bank and supermarket executives.

“I think it’s been the Telegraph’s dirty little secret for some time,” one former Telegraph executive told Press Gazette.

“There is a wider culture where it’s been taking place for some time where key advertisers and key clients senior executives at the Telegraph really can’t afford to offend them.

“And that might mean stories being softened, stories being downgraded in terms of placement, headlines softened or stories not run at all. And I think that’s been going on for some time.”

They said that not all reporters are aware of the commercial sensitivities and that the influence is “subtler than that”.

Asked if they believe these commercial pressures exist at the same level on other newspapers, they said: “I think it goes on far more at the Telegraph than elsewhere.”

Press Gazette was told by another well-placed source that the picture painted by Oborne was entirely accurate. Oborne claimed that negative stories about HSBC have been discouraged at the Telegraph since the start of 2013.

The source said that the division between commercial and editorial on the paper had "completely broken down" and that it was now normal for commercial staff to attend news conference and then talk to reporters directly about stories, emphasising which companies are major advertisers.

Telegraph insiders have noted the close relationship that both chairman Aidan Barclay and chief executive Murdoch MacLennan apparently have with senior bankers and supermarket executives.

A well-placed source said that the HSBC advertising account with the Telegraph was worth £3.5m a year.

One example of alleged commercial pressure brought to bear on editorial involved a story published on 10 December 2013 about Royal Bank of Scotland chief executive Nathan Bostock quitting the bank after ten weeks in the job.

Press Gazette understands that the website story headline, “RBS thrown into turmoil by finance director quitting”, was “toned down” in the print edition and that the reason given by the senior executive demanding the change was “they are major advertisers”.

The print edition headline read: “RBS finance chief Nathan Bostock quits after just 10 weeks”.

Press Gazette understands that editorial executives have also come under pressure about pieces by columnist Allison Pearson which have been critical of Marks and Spencer.

A long-serving writer for the Telegraph, who is no longer with the paper, said: "On the newsdesk and in the newsroom there was a lot of interference."

A former senior executive involved in daily production of The Daily Telegraph told The Times: "If there was as story related to a big Telegraph advertiser and something that was deemed critical was going to appear, subsequently you'd get a call of irritation from someone very senior saying: 'We've heard that you might be running a story about Tesco… Did you know that they spend X amount with us advertising each year?

"'And can you take extra care over the story? And do we really have to run the story? And do we have to run it this way?'"

Newsnight's Chris Cook said in a report last night: "We've spoken to more than a dozen current and recent writers, editors and reporters from the Daily Telegraph. They all say that while they may quibble with a fact or two in Peter Oborne's piece, it is 99 per cent right."

Speaking in London in April last year, Telegraph editor in chief Jason Seiken spoke about how an editor must bridge the "sacred divide" between commercial and editorial departments "helping to devise new revenue streams, nurturing and developing relationships with advertisers and partners but always ensuring and protecting the editorial integrity of the institution and the journalists".

But he also spoke about the importance of defending the integrity of the Telegraph brand.

He said: "Our approach to continuing to transform the Telegraph for the digital age rests on two fundamental principles: The first is one we've had all along – the principle that our most valuable asset is the iconic Telegraph brand.

"A brand that stands for integrity, honesty, reliability, and trust.

"Regardless of how the technologies change, these are immutable and non-negotiable, and that brand is our biggest asset, both in print and digital.

"The second principle is this: We will create a culture where, bucking the weight of 159 years of tradition, the only commandments chiselled is in stone will be those core values of integrity, honesty, reliability, and trust.

"Everything else is open for experimentation and change as we disrupt ourselves into the new golden age."

The Telegraph statement in full: