When Boris Johnson became an MP in 2001, it was noticed that for all his worship of Churchill, and facility with words, Boris was unexpectedly not much good in the chamber of the Commons. This was surprising, to those of us (me included) who liked his pluck and “feelgood” routine. Boris is one of the funniest and most powerful speakers around, given 15 minutes to prepare and a pen and a piece of paper on which to scribble. But something about his unique style (too freeform? too funny in an uncontrolled manner?) has never translated to Westminster. Being at the despatch box as Foreign Secretary has only made this more obvious.

Perhaps it is appropriate then, in a taking back control type way, that it is the chamber of the House of Commons, or some of the MPs in it, who may have finally done for Boris. Very few Tories turned up to support him today, and he was duffed up comprehensively under questioning about his potentially disastrous blunder in the case of Nazanin Zaghari-Ratcliffe. She was detained 18 months ago by the Iranians and is in prison there after being convicted of unknown offences.

Last week, giving evidence in front of the Foreign Affairs Select Committee, Johnson said:

“When I look at what Nazanin Zaghari-Ratcliffe was doing, she was simply teaching people journalism, as I understand it. “[Neither] Nazanin Zaghari-Ratcliffe nor her family has been informed about what crime she has actually committed. And that I find extraordinary, incredible.”

She was not teaching people journalism, she was on a family visit, but four days after the Foreign Secretary’s comments Nazanin Zaghari-Ratcliffe was brought back to court to be told that this – her alleged role in pushing anti-regime propaganda, which she denies – could mean up to another five years in prison.

Johnson had blundered, riffing about “teaching journalism” rather than sticking to the facts of the case and learning the Foreign Office line to take. The family and MPs from all parties were furious. Here was something much worse than a gaffe. Here was a comment that could cost an innocent women several more years in an Iranian prison. Johnson will – no doubt, privately – be mortified.

But, for reasons which will no doubt be explained in his memoirs, Johnson decided not to apologise and correct the record swiftly, which would have been sensible. Thus he came to the Commons on Tuesday to admit only that “he could have been clearer.” That’s the problem: he was perfectly clear, we saw it. Caught out, he has stuck with an explanation that holds no water.

MPs were coruscating in their condemnation today. Boris looked by turns leaden, lost and tone deaf. As a result of the row, Shadow Foreign Secretary Emily Thornberry’s moral superiority complex is in complete overdrive. She senses that he is a goner.

She may be right, and he faces an almighty struggle to reassert himself. As of now, Boris looks bust, his goose cooked, his ship sunk. Unless he can negotiate the release of Nazanin Zaghari-Ratcliffe, and soon.