I have been worried about the Daily Mail's editor, Paul Dacre, for some time. After seeing today's issue of his paper, I really think it's time for the men in white coats to visit its Kensington offices as soon as possible.

The Mail devotes 11 full pages, including the whole of the front page, to a "special investigation" into one of the Leveson inquiry assessors, Sir David Bell.

It seeks to present Bell, the former Financial Times chairman, as the spider at the centre of a web of intrigue. In a classic example of conspiracist innuendo, it implies that the "elitist liberal" Bell is covertly exercising influence that somehow threatens the freedom of the press.

He is presented across many thousands of words as some kind of shadowy figure who, through his chairmanships and trusteeships of various charitable bodies, is exerting undue and unaccountable power.

Through a series of leaps of logic and phoney "revelations" of Bell's publicly acknowledged positions, the articles persistently insinuate that he has been up to no good.

He is even accused of being somehow responsible for the Newsnight report which falsely suggested that Lord McAlpine had been guilty of child abuse and, by extension, that he is also part of the reason for the BBC's current crisis, including the resignation of its director-general.

In a leading article, the Mail says its "investigation paints a picture of how a small, intertwined nexus of Left-of-centre individuals – some with links to Ofcom, the media regulator, and virtually all with links to Bell – have sought to exert huge influence on the inquiry."

Clearly, this is a sensitive time to attack a member of Lord Justice Leveson's team, as the editorial admits:

"The Mail is acutely aware of the seriousness of publishing this investigation. We know all too well that our enemies will accuse us of being aggressively defensive in a bid to pre-empt the outcome of the Leveson report, which is due any week now. But in the light of the scandal engulfing the BBC, we passionately believe in the public's right to know about a senior Leveson assessor's role in it."

So, in order to lend some sensible perspective to this astonishing accusation about Bell's supposed complicity in the BBC's "scandal", let me try to disentangle what amounts to a farrago of distortion with added vilification.

First, Bell is a trustee of an organisation called Common Purpose, a charity that runs leadership development programmes. Its chief executive is Julia Middleton.

Second, Bell was the inaugural chair of the Media Standards Trust (MST), a campaigning body supported by charitable donations that was set up in 2006 to address concerns about a deterioration in journalistic standards. It has been acutely critical of the Press Complaints Commission. It is also connected to the Hacked Off campaign group.

Third, Bell is a trustee of the Bureau of Investigative Journalism (BiJ), a journalistic venture created in 2010 and funded by a philanthropic grant. It was responsible for the inaccurate Newsnight report that wrongly implicated McAlpine as a paedophile.

None of these activities are covert. Bell also happens to be chair of the council at Roehampton University, chairman of Sadler's Wells Trust and director of the global social enterprise group Imagine Nations. He is what is generally known as a do-gooder.

The Mail, however, casts him as a do-badder. It implies that he, Middleton, and several other people connected to them through lobbying, PR groups and Ofcom constitute a covert network of "incestuous relationships" that, in various ways, are linked to the Leveson inquiry. These include fellow assessors and inquiry witnesses.

Given the length of the Mail investigation, it is impossible to deconstruct every false link and illogical innuendo, but let's look at one - the implications of Bell's trusteeship of the Bureau of Investigative Journalism (BIJ).

The bureau came to life as the result of a £2m grant from Elaine and David Potter. They are the bureau's trustees along with Bell and George Brock, the head of the journalism department at City University London, which provides the BIJ's accommodation.

As trustees, the four have been at arm's length from the daily operations of the bureau itself. Until the Newsnight debacle, the bureau had been noted for the quality of its journalistic output. It had previously won awards and it was recently nominated for four of this year's British Journalism Awards.

When the Newsnight mistake occurred, in circumstances that have yet to be explained, the trustees met and the bureau's managing editor, Iain Overton, resigned. The reporter concerned, Angus Stickler, has stepped aside. It was rightly said that the Newsnight segment was an example of "shoddy journalism" and it's possible that the episode may imperil the bureau's future.

But Bell's link, as a trustee, cannot be said to be anything other than tangential.

Similarly, Bell is also smeared by the Mail over the Media Standards Trust's running of the annual Orwell Prize because, in 2008, it was awarded to The Independent journalist Johann Hari. It transpired years later that he was guilty of plagiarism and he returned the prize.

All that having been said, the Mail does raise some questions about Bell that certainly do deserve attention.

For example, Bell is a trustee of the Esmee Fairbairn Foundation, a grant-giving charitable trust that provided a generous grant to the MST (though it was given prior to Bell joining the trust's board).

Furthermore, Bell is chairman of the Pearson Foundation, a charity that also gave a big grant to the MST.

Though there was no attempt to conceal these grants, and Bell's links to the foundations were not secret, it does appear to me that being a trustee of a body giving grants to a body that he chairs is inappropriate.

However, this particular point aside, the rest of the accusations, allegations and insinuations about Bell, Middleton and a variety of their colleagues and acquaintances appear well wide of the mark.

For a national paper to devote the best part of a dozen pages to an investigation so obviously based on prejudice against the Leveson inquiry is surely counter-productive.

It is very likely to reinforce the view of politicians that the Mail's brand of journalism is too often born of bias. And that that bias is located in the person of its editor.

How is it defensible to talk of "freedom of the press" in the collective sense when a single man exercises so much power? The likeliest effect will be to convince MPs that statutory press regulation is a good idea.

Belated full disclosure: I teach at City (I tend to overlook it because I play no part whatsoever in the university's admin. I lecture and I mark. That's it). See also: 11 surprising revelations in the Daily Mail's anti-Leveson hatchet job in the New Statesman and in Mail declares war on Leveson and warns of left-wing 'coup' in The Week