To listen to Oliver Letwin’s speech of Tuesday – which we have a video clip of, if you missed it – is to gaze a long, long way through the constitutional looking glass.

In it, he admits to what had previously only been hinted at: that if the House of Commons passes the bill known as ‘Cooper/Boles’, the legislature will fundamentally usurp the proper role of the Government in running the country.

As he puts it, the House of Commons will be the Cabinet. It would be, as he acknowledges, a situation almost certainly unique in the uniquely long history of Parliament as a representative institution. He asserts, perhaps sincerely but inevitably falsely, that this upheaval would be temporary.

Brexit has prompted a huge volume of writing about the constitution, and spurious allegations of ‘constitutional outrages’ are not hard to find. But the consequences of what Letwin and his confederates propose are truly mind-boggling.

Earlier this month, I wrote about the unwisdom of the ‘Meaningful Vote’ as a constitutional innovation. So much of the incoherence which critics of the Government claim are making the UK a laughing stock on the international stage are rooted in the fact that the Commons has deprived ministers of their normal powers to conduct foreign relations and conclude treaties.

Of course, the impact of the Meaningful Vote pales in comparison to what Letwin proposes to unleash. But they each have their roots in the same dogma: that it is right and good to expand the power of the House of Commons, regardless of the circumstances.

So let’s consider just some of the issues raised by the Cooper/Boles plan to “fundamentally realign the relationship between civil service, government and parliament”.

As Letwin admits, the plan will take more than one law to take effect. Once underway the establishment of what will effectively be a wildcat executive will require further legislation, introduced by backbenchers and imposed on the Cabinet. The more of this there is, the more fatuous suggestion that the consequences will be containable: both the precedent and perhaps much of the legislative architecture of the Letwin Ministry will remain in place, to be wielded against any future minority government.

Moreover, what becomes of the actual ministers? Are they expected simply to remain obligingly in office, rendered an extension of the civil service as they wield executive power at the behest of the government-once-removed? To remain politically accountable for the policies of a shadowy parallel executive?

And not just politically accountable: all the mechanisms our system has evolved for scrutinising executive decision-making will remain trained on Ministers of the Crown. It is they, and not the officers of the new order, who can be called before the House, field questions, and so on. Yet what is the point of quizzing the Prime Minister, or indeed any Secretary of State, on Britain’s Brexit policy if they are not directing it?

As Letwin acknowledges in his speech, the actual Government is accountable to Parliament. But if Parliament becomes the Cabinet, what steps up to take the role of Parliament? There is nothing, save perhaps the judges and political scrutiny is not their function.

That’s just a small portion of the questions thrown up by these proposals. Elsewhere Nikki da Costa, the parliamentary and procedural expert, has sketched out an entirely distinct, political problem with how the Cooper/Boles plan would severely degrade not only procedural scrutiny but political accountability to the electorate.

It’s all worth a read, however right at the end she hits on something particularly important.

There’s a reason that the measures Letwin is advancing have not been tried before, and it is not because this country has never before faced a serious crisis. It is that the House of Commons always has the power to dismiss a government in which it has lost confidence, and either install a new one or take the argument to the people. Even outside a formal vote of confidence individual MPs can resign the whip or even cross the floor, should they wish.

But doing so involves taking responsibility: for renouncing your party loyalty; for withdrawing your confidence in the Government; for taking your case to the country.

Cooper/Boles, by contrast, involves deliberately maintaining a public-facing theatre of constitutional normalcy – of confidence in Her Majesty’s Government; of ministerial responsibility; of the party system; and so on – whilst wresting and then wielding power beneath it, far removed from all established mechanisms of scrutiny and accountability.

You cannot honourably claim to have confidence in the Government whilst usurping its power to direct policy on the single most crucial challenge facing the country. The Prime Minister would be within her rights to treat Cooper/Boles as a de facto confidence measure.