The fall of Michael Fallon is a mighty blow to Theresa May. Her rickety government has just lost one of its old reliables. She could send him out there on Today or Newsnight and he would spout the line of the day faultlessly, unblinking. Even if the line was palpably, laughably absurd, he could say anything with a deadly straight face, a solemn bearing, and an articulate pomposity that had at least a veneer of plausibility.

When other cabinet ministers vanished down rabbit holes hiding from incoming fire, the defence secretary would go out there willing to swear that day was night and black was white, even when he knew the policy was so impossible it would change hardly before he’d left the studio.

For those who remember the hours of the fall of Baghdad, he was our Comical Ali, the absurd character willing to swear there were no US troops on the streets, no mobs pulling down statues of Saddam Hussein – though you could see them in the background. Every prime minister needs one of these, and May has just lost hers. She has pitifully few stalwarts in her cabinet of conspirators and she can’t afford this.

Was he brought down by Julia Hartley-Brewer’s knee? “I doubt my knee was the reason,” she said on Twitter, since, ferocious Tory that she is, she never said she was much bothered by the knee incident anyway. Whatever it is that caused his resignation, there were hints of it this morning when May failed to give him wholehearted – or any – kind of support. The wording of his departure suggests more, and no doubt it will surface. “In the past I have fallen below the high standards we require of the armed forces.” How far below? More than a knee-touch, surely.

There will be shudders through Westminster’s ranks. The circulating list of Tory harassers and sexual malefactors may or may not be accurate, but there are quite enough MPs who will fear their own head may join Fallon’s on a Westminster spike. A government this perilously fragile, only a scandal or two away from losing power. Macmillan staggered under the Profumo affair, John Major was felled by his “back to basics” morphing into serial sleaze.

What an irony it would be if another good old British parliamentary sex scandal brought down this government – and not the Brexit abomination or the extreme suffering caused by austerity or any of the myriad acts of atrocious governance they have been guilty of since 2010.