Last night’s defeat, and attendant humiliation, for the Government has inevitably inspired a fresh bout of recriminations. Variously, blame is placed at the door of the Prime Minister (for messing it up), the Whips (for not being prepared for all eventualities), Gavin Barwell (for allegedly telling Remainer ministers they could disobey a three-line whip), and so on, and so on.

Perhaps all of this is justified – much of it certainly is. But different aspects of it matter more than others. It’s obviously woeful that the Prime Minister has led the Government into such a state. It’s dreadful that the Whips weren’t on top of their job. If it’s true that Barwell encouraged or facilitated ministers ignoring the whip (which he denies) then that is positively outrageous.

But we knew already that May’s leadership is a bombsite, and that the Whips’ office has been stripped of experience and authority. If the claim about the Prime Minister’s Chief of Staff behaving so badly is true, then while it is appalling he will at least be departing when his boss does. There’s not much new to these elements of the sorry saga, nor does it change much for the future of the country or the Conservative Party.

The actions of those ministers who breached collective responsibility by ignoring the Whip and abstaining are a different matter, however. Most of them hope and expect to have a future in Government, perhaps even climbing further up the ladder than their current rung.

And yet how can that possibly be, when they have demonstrated publicly that they are willing to undermine the Government of which they are part, in a whipped vote, and still try to hang onto their ministerial jobs? The fact they have not been sacked is a reflection only on the weakness of the Prime Minister, not on the severity of their offence. Such a breach threatens to deal a severe and lasting blow to a key principle of our system of government, namely that ministers stand together or fall apart.

In practical terms, how could a future Leader or Prime Minister trust them not to repeat the same trick on this or another issue? How could their Parliamentary colleagues be sure that when they answer the call and pay a price among voters for supporting controversial or unpopular policies, ministers won’t then sell them out by voting as they fancy rather than as they have promised? How could voters, already understandably sceptical of politicians’ promises, be persuaded to believe a manifesto, or a Prime Minister’s word, ever again? The lack of trust would be corrosive at every level of politics.

It isn’t good enough to say “Gavin said it was fine”. Whoever you get advice from on a three-line whip, it’s still a three-line whip – particularly if the advice you’re getting isn’t from the whips. Nor does it suffice to say “Well, it was a confusing situation.” You are not novices, you are experienced ministers, including Cabinet Ministers. I’ve seen the text messages sent out making the position clear, and even if there was a miraculous outbreak of phone failure, there are whips and other colleagues available on the spot to check with.

The fact is that it was a three-line whip; I am yet to see any reason to believe that was not known, and therefore it was a conscious decision. Rather than any excuse, the justification simply seems to be David Mundell’s line to Sky News last night: “Because I feel strongly.”

All MPs have the right to feel strongly, of course, and have the right to act on that feeling. Ministers, however, have a binary choice – if their strong feeling conflicts with the requirements of being in Government, then they can adhere to collective responsibility and swallow their feeling, or follow their feeling and resign from office. Many people have done so honourably, for far less.

That principle matters and is necessary for the good functioning of government. We can see right now what things would be like if it was lost permanently.

The normal sanction for breaching it would be a prompt sacking by the Prime Minister. In the absence of the will, capacity or authority on the part of the current Prime Minister to do so now, it should instead be carried out by her successor. It’s impossible to see how ministers who behave in this way could be trusted again, and a promise not to repeat the behaviour would bear no more weight than the original promise not to do it in the first place.