Dominic Cummings failed to wing Boris Johnson with his first barrel. It’s not at all unlikely that he’ll have better luck with his second.

The first shot was the Downing Street redecoration controversy, about which the Prime Minister’s former special adviser tweeted and substacked energetically.

Christopher Geidt could have ruled that Johnson had breached the Ministerial Code, and the affair had the potential to draw in Kathryn Stone, the Parliamentary Commissioner for Standards, and perhaps the police.

However, Geidt decided otherwise, and Stone is not investigating.  Which brings us to Cummings’ second shot.

Last week, he wrote to draw attention to the systemic importance of the Prime Minister’s Private Secretary…and, separately, about a party in the Downing Street garden on May 20.

The dots were duly joined in last weekend’s Sunday Times, in which Martin Reynolds, Johnson’s Private Secretary, was revealed to be the organiser of the event. Number Ten hasn’t denied that the Prime Minister was present.

Reynolds’ e-mail to some 100 staff members said that “we thought it would be nice to make the most of the lovely weather and have some socially distanced drinks in the No10 garden this evening”.

“Please join us from 6pm and bring your own booze!”  Politico’s daily newsletter has a list of quotes from Ministers from the period making it clear that gatherings of more than two people were against the Covid rules.

The key point is that this is the first “staff gathering”, to use the terms of Sue Gray’s investigation into these, both to have been formally designated a party and at which the Prime Minister was present.

Or at least of which we are all aware.  There are at least five potential further developments, all of which would have knock-on effects on each other, like billiard balls in a snooker game.

First, there is the question of whether Johnson has misled the Commons over his attendance at Downing Street parties.  Second, this particular one draws Johnson more directly into Gray’s report.

Third, there is the possibility of police action (the Met has been in contact with the Cabinet Office).  Fourth, Conservative MPs will be put on the spot by any Labour motion of censure.

Fifth, an increasingly restive Cabinet will react to any combination of the above.  As, sixth, will any Tory MPs minded to write to Graham Brady in order to demand a ballot of confidence in their party leader.

To predict precisely which billiard ball will hit the others, and where any of them might go, is less useful than giving a sense of why this particular party is more problematic for the Prime Minister than other “staff gatherings” to date.

It’s worth noting that we are unlikely to have heard the last of it and of others.  The Hancock video footage, the seperate photo of Downing Street garden drinks…”the hits just keep on coming”.

The Met will be very reluctant to be drawn in – and remember that Cressida Dick’s own position as Commissioner is precarious.

It may well be that Johnson will sag downward on the long zipwire of his career only to lurch up again, and continue his odds-defying political journey, perhaps even to another big election victory.

But for all its differences, the Number Ten “staff gatherings” have about them a smack of the MPs’ expenses scandal – at least in terms of public reaction so far and going forward.

True, “expenses” was cross-party.  And – true again – the Commons had no coherent grip on the system, whereas government, Ministers and civil servants alike, have clear control of the rules and the law.

Nonetheless, what the two have in common, at least as far as the mass of voters are concerned, is a sense of entitlement: of an establishment that flouts laws it makes for others and treats them with contempt.

What will perhaps concern Tory backbenchers most is that Number Ten appears to have no coherent defence. The best it can apparently offer to date is that the Prime Minister is entitled to use his own garden.

The rules may say one thing – as may the law – but politics says another, namely: that this simply won’t do.  Time to adjust your seat-belts.

For better or worse, big staff changes are coming at Number Ten in the wake of Gray’s investigation.  Downing Street has no option but to take it on the chin and go with the flow: after all, it’s in limbo anyway.

And Johnson now has little choice but to shake up his political team.  I doubt that will help and could well harm.  Either way, it may not be enough.  His fabulous luck has a high melting point, but the heat of this fire is searing.