David Frost’s resignation letter won’t force Boris Johnson’s departure.  Sue Gray’s investigation into Downing Street staff gatherings could.  So the media attention the first is commanding compared to the second is disproportionate.

How might Gray bring about the end of the Prime Minister?  I make a preliminary point.  When Simon Case had charge of the investigation, some expected its findings to come very quickly.  For until they do, Downing Street can scarcely function – because no-one knows who, like Allegra Stratton, will soon be required to resign.

And  Gray doesn’t conclude her inquiry early in January, the ensuing uncertainty will further destablise Number Ten’s handling of Omicron. Now to the investigation itself.  Here are two plausible versions of how it could conclude.

The first is that there is no definitive proof that the Prime Minister broke lockdown rules, because of the ambiguity of what counts as a social gathering.

The second is that he was indeed in breach of the rules: for example, that the new photo of him drinking wine with staff in the Downing Street garden shows a party, not a meeting. Or that whether or not he was a rule-breaker, he was responsible for a culture of law-breaking.

Much may turn on what Gray decides does and doesn’t constitute a “staff gathering” – the term used in the terms of reference to her investigation.  And if her findings are published in full, if at all.

So what is she likely to conclude?  Understanding the answer means understanding Sue Gray, or rather how she has acquired a fearsome reputation as a despatcher of Ministers.  In a nutshell, Gray is a quintessential product of the post-Nolan state: one of a cluster of powerful bureaucrats – a blob, if you like,

These include the Independent Adviser on Ministerial Interests – currently Lord Geidt, charged with investigating the Downing Street redecoration saga, who has gone very quiet recently.

Some of these are creations of the Blair era; others the product of the Major Government, created in the wake of the “cash for questions” affair.  Gray does not currently hold this kind of post: she is listed as second Permanent Secretary at the Cabinet Office.

But she did, as the first Director General, Propriety and Ethics: a civil servant based in the Cabinet Office charged with “ensuring the highest standards of propriety and ethics across all government departments”.

The role was invented by Jeremy Heywood, the former Cabinet Secretary and Head of the Civil Service – and formidable Whitehall operator.  Its holder wields discreet power: for example, he advises on “the policies and codes governing ministers and special advisers”.

Andrew Gimson’s profile of Gray for this site, written in 2017, quotes Oliver Letwin, himself by temperament, though not of course by occupation, a civil servant, and a man with coalface knowledge of Whitehall insidery.

“It took me precisely two years before I realised finally who it is that runs Britain,” Letwin wrote. “Our great United Kingdom is actually entirely run by a lady called Sue Gray, the Head of Ethics or something in the Cabinet Office…unless she agrees, things just don’t happen.”

But the complaint that dogged Gray, during her time in the post, was not so much about her responsibilities as the way she exercised them.  They are crystallised in this piece about her by Chris Cook.

In sum, Cook suggested that Gray was reluctant to commit decisions to paper, and therefore in a position to make up the rules as she went along.  Readers may remember a case he cites – how a refusal by Gray to make a ruling resulted eventually in a bar on Nick Timothy and Stephen Parkinson as Conservative Parliamentary candidates.

Later, Timothy became Theresa May’s co-Chief of Staff and Parkinson her Political Secretary.  I’ve spoken to the former in the course of researching this article, and to three Ministers who left Government during her tendure.

The consensus is favourable.  One claims that Gray as “has a Blair-era mindset and is instinctively anti-Tory”.  By contrast, another says that “I found her very straightforward to deal with.”  A former Cabinet Minister who worked with her gives the same verdict.

She was in place during the so-called “Plebgate” row which resulted in David Cameron firing Andrew Mitchell – who is full of praise for Gray, describring her as “a civil servant of the highest integrity”.

All of which poses the question: since not all takes on her are so favourable, why on earth has the Prime Minister granted her the potential power of life and death over him – in political terms, at least?

I don’t know, and sometimes there are wheels within wheels.  But an explanation I’ve been offered is, first, that Labour cannot credibly accuse Gray having any bias in favour of Johnson.  That, second, he is in no position to have resisted the suggestion, wherever it first came from.  And that, third, he believes he’s done nothing wrong.

Whatever she concludes about the Prime Minister, one view is that her investigation will finish off Simon Case – the Johnson/Cummings era appointment as Cabinet Secretary and Head of the Home Civil Service.

Why? Because, in the words of one source, “unlike her and the establishment, Case is not a product of the Heywood machine, which wants to take back control of the system”.  But I’m not convinced that Gray is part of any club, let alone of a Treasury-based cluster of mandarins.

For it’s worth noting that she doesn’t actually run a department.  One source says that she has made recent applications for such posts, but I cite this claim with a questionmark.

Gray may not a member of a club but she is certainly a member of a class, at least in my view – one that takes in the sweep of her career since her responsibility for propriety and ethics.  The image I’ve accumulated of her, in the wake of talking to others about her, is of a woman who sees herself as a kind of modern-day Platonic Guardian.

Classically-minded readers will remember that Plato was critical of Athenian democracy, which was faring poorly during the Peloponnesian War.

He believed that the state should be governed by an elite of philosopher-kings, later known as Platonic Guardians.  And his hero was Socrates, a new Achilles of self-mastery, dispassion and wisdom, not Homer’s original Achilles of passion and impulse.

One of many battlefields in the culture war sees the elected, people we can hire and fire at the ballot box, exalted above those we don’t: see Paul Dacre’s rage against the machine over the Ofcom appointment.

Or heed the call of Jonathan Evans, the Chair of the Committee on Standards in Public Life, for his post and that of the Independent Adviser on Ministerial Interests to operate “on a statutory basis”.   Above all, follow Matthew Elliott’s accounts on this site during David Cameron’s premiership of the struggle over appointments.

A Cabinet Minister told me that Gray won’t leap “the high bar of destabilising a Prime Minister”.  That may well be right.  But she will surely be mulling, as she prepares her report, what the future may hold for her – and how the apples would roll if the apple-cart toppled over.

Were the Heywoods and Evans’ to be taken back in time and dressed up in togas, they might well describe Achilles, with his child-like passions, as “not a serious person”. Or “not a grown up”.

And whatever else he may be, Johnson is an Achilles, not a Socrates.  Does Gray believe that he is fit to govern?  After all, she is a Platonic Guardian, if not exactly a Platonic Guardian.