First things first.  The Prime Minister is absolutely entitled to fire a Minister who leaks, and approve a more exacting than usual inquiry to identify the culprit.  Her Cabinet is unprecedently non-watertight.  Some of its members not only give journalists a read-out of its proceedings afterwards, but offer them a briefing beforehand – complete with details of what they are about to say.  We hacks love it.  Number Ten hates it.  One understands why Mark Sedwill and Theresa May want a crackdown.  That they leak stories themselves in no way invalidates one.  The old Whitehall saying comes to mind: I brief; you leak; he is in breach of the Official Secrets Act.

So Sedwill’s probe was justifiable.  But was it wise?  That is less certain.  Yes, a leak from the National Security Council is serious.  But information has dribbled out before.  Clashes within it over military intervention in Libya got into the papers in 2011.  More recently, friends of Williamson suggest that Sedwill himself was responsible for the emergence of details about troop numbers of Afghanistan.  Nor in this case can the former Defence Secretary or anyone else be accused of revealing operational secrets.  What emerged was details of a policy debate, the conclusion of which would have become public in any event.

There is another reason why the scale and reach of this inquiry may have been an unforced error.  Sure, Sedwill seems to have been convinced that Williamson has form as a serial and serious leaker.  And the decisiveness of his sacking momentarily summons memories of May in her pre-2017 general election days, when she led with authority.  The timing of the former Defence Secretary’s dismissal, bang on the verge of local elections day, may even do her a little good.

But the bottom line is that though the timing of Williamson’s eleven-minute conversation with Steve Swinford, the Daily Telegraph journalist who broke the Huwaei story, is suggestive, it isn’t conclusive.  Downing Street cannot prove that the former Defence Secretary was Swinford’s source – or if it can, the evidence it will have is unlikely to be the kind that can be made public.  May says Williamson’s guilty. He says he’s innocent, and is on the counter-attack, claiming that Sedwill is waging a vendetta against him.

Number Ten will want to bag much of what it has won so far: firm action, quick headlines, a Ministerial scalp.  It will now hope to move on rapidly, with no police inquiry or criminal prosecution.  The former Defence Secretary is making this just a bit more difficult by refusing to go quietly.  Whatever happens next, Downing Street will be under pressure to release more details of “the manner in which [Williamson] engaged with the investigation”, as the Prime Minister’s farewell gnomic letter to him put it.  It may not want to get into them.

So, then: who do you believe – or perhaps rather, who do you want to believe?  Some Conservative MPs don’t like the former Defence Secretary, believing him to be insubstantial, erratic, conspiracy-prone, a fantasist who can’t tell the difference between real political life and House of Cards – and a boy doing a man’s job.  In the light of which, we point out that, among Tory MPs, the defence post is hugely prized.  It has almost the status of a great office of state.  When we last did a count, over 50 MPs had served in the armed forces.  Most of them are Conservatives.  When Williamson was first promoted, many of them thought they could do a better job at the department than a rookie.  Bear that in mind when you read the briefings against him.

Others dislike Sedwill. Watch for the politics of this sacking to become entangled with the politics of Brexit, the Tory leadership –  and Downing Street’s new and unusual Home Office culture, with its stress on safety and secrets.  Number Ten sees a lot of policy through the lens of security: “the most high-profile pronouncements from the current Government on the internet seems to have been not about maximising its contribution to the economy, but on the Internet as Social Menace,” Sian Westlake wrote recently. “Issues that have been granted political airtime include banning encryption, regulating pornography and cracking down on businesses like Deliveroo and Uber”.  Brexiteers, civil libertarians and May’s opponents all have reason to target the ex-Home Office Cabinet Secretary.

This morning, the Prime Minister has a former Chief Whip on the loose – one, too, who was a player in her own leadership election team back in 2016.  Williamson not only knows where the bodies are buried, but why they were concealed in the first place – and who was responsible.  To borrow his own words, he is unlikely now to “go away” and “shut up”.  That may have consequences for the Government and for May herself.  What’s that you say?  That all this is of second-order importance – and that what really matters is the Huawei decision itself?  Quite so.  And on that, regardless of his accuracy elsewhere, we have an uncomfortable feeling that Williamson is right.