A few weeks ago I highlighted the possibility of Parliamentary moves that would potentially undermine the constitutional basis of British government.

So it proved last week, when the Commons overturned its long-established rules of procedure to allow a Bill to avoid a "no deal" Brexit, laid by the backbench MP Yvette Cooper, to be given a second reading. It passed almost immediately through its Commons stages, and is presently being debated by the Lords.

It is likely very soon to become law. So far backbenchers have acted with some circumspection. But soon they may move to more substantive matters. If they do, we will witness an extraordinary sight.

A Government democratically elected on a manifesto commitment to deliver a Brexit outside the Single Market and Customs Union, in an orderly and agreed way, could find that policy overturned by backbenchers who have no corporate standing to do so.

They would be, let us be clear, a group of individuals who have temporarily made common cause, forming no political party, offering the electorate no policy at the last General Election, with no collective mandate of any kind.

They would have no executive capacity. In no other respects would they act together. They would thus be in the purest sense a Parliamentary faction, lacking the basic ingredient of any proper parliamentary grouping: political legitimacy.

People have voted in general elections in this country for more than a century on the basis that the elected Government of the day has the democratic right to put its business, especially manifesto commitments, to the Commons ahead of other petitioners. These changes threaten to destroy that established understanding.

More deeply, since the "Glorious Revolution" of 1688, from which the sovereignty of the Crown in Parliament was created, the greatest achievement of British politics has lain in its movement towards what the philosopher and historian David Hume called “a government of laws, not of men”.

The British constitution thus evolved a unique combination of flexibility and authority, which has been widely envied and imitated. In general, contrary to recent reports, it still works remarkably well.

As I wrote earlier, the central point of our constitution is to allow the passions of politics, referenda or no, to be channelled through Parliament. But Parliament works according to rules ratified by experience and history. Leave those behind and you sail in uncharted seas, at your peril.