Sometimes it is the smallest things that speak loudest.

For all the heavyweight criticism of Rupert Murdoch’s News Corp over its partisan coverage of national affairs (we will skip the allegedly), a telling blow to its credibility has landed from a most unexpected quarter.

Peter Farrell, of Monarto in country South Australia, is no ideological warrior. In fact he describes himself as “not a political person; I don’t particularly support either side”.

Yet he has called News to account in a most enlightening little episode.

As revealed on Media Watch, Mr Farrell wrote a 35-word letter to The Australian several weeks ago linking ABC chief Mark Scott, Labor senator Stephen Conroy and former prime minister John Howard under the subject “Sorry trio”.

They were, he conceded, “strange bedfellows”. He continued: “But they share one characteristic, in common with many who combine soaring ambition with acute self-belief. All refuse to utter the word ‘sorry’.” That was it. Short and sweet.

Imagine Mr Farrell’s surprise when he opened his Australian to discover that his trio had been reduced to a duo.

Mr Howard had been excised, leaving only the ABC and Conroy as the subjects of Mr Farrell’s criticism.

It almost goes without saying that the uninvited editing of the letter brought it into closer line with The Australian’s editorial position.

The paper has been conducting a relentless campaign against the ABC and Labor, with Scott and Conroy particular targets.

It is one thing – and entirely legitimate – for the paper to rail against the ABC and Labor in its editorials (Last Friday, for example: “Labor has become so backward in its economic thinking that it even appears to be somewhere to the Left of ABC questioners”).

It is altogether another matter for the paper to doctor letters from private, fair-minded citizens to misrepresent their position and to better suit its own.

The paper’s response was, frankly, pathetic.

It should have been: “We apologise to Mr Farrell and our readers for distorting his position. The editor concerned is being counselled.”

Instead, letters editor Graeme Leech told Media Watch: “Yes, John Howard’s name was edited out because he has been out of office for more than six years whereas Scott and Conroy are still in the public eye over whether or not they should apologise.”

Mr Farrell was not impressed, telling Media Watch: “It seems obvious to me that the letter was edited so it fell completely and unambiguously into line with their current editorial position – i.e. anti-Labor, anti-ABC.

“People at the Oz should realise that just because someone subscribes to their paper (which I do), it doesn’t necessarily mean they are happy to be portrayed as another right-wing warrior (which I’m not).”

The response from News if the ABC or Fairfax had pulled the equivalent stunt in reverse would be nothing short of feral.

The Australian’s ideological goggles are on so tight, and the groupthink within the organisation about its enemies so pervasive, that this sort of conduct becomes possible. Worse, it attempts to justify it when caught out.

Much of the criticism of News is deflected on the basis that it comes from the inner city “green-Left” that it so despises, academia, commercial rival Fairfax or, even worse, the ABC.

Mr Farrell would not appear to belong to any of these tribes. He just wanted to write a letter to the editor.

That is why his treatment at the hands of The Australian is so telling.

Patrick Smithers is the sports editor of The New Daily and a former sports editor and executive news editor of The Age.