Hitherto one of the striking things about Brexit has been that it has been debated, however rancorously, through the medium of normal politics.

Yes, the EU referendum in 2016 was unusual, but it was hardly unprecedented. Tempers have run high, there have been all kinds of to-ing and fro-ing in the House of Commons, but the British constitution—the political “rules of the game”—has held.

All that changed last week, when the Speaker broke with established procedure to allow an amendment to a Government motion that had been put “forthwith”, on the future business of the House.

There was an argument, the winners celebrated, the losers complained, yada yada yada… so what?  In fact, so much hangs on this that it is important to spell out what happened, and why it matters.

Historically, the settled agreement of the House of Commons over many decades has been that such “forthwith” motions are not debated or amended. Literally thousands of them have been put and voted, for or against, on this basis—including last week.

The Clerks of the House, who are the impartial experts on the rules, gave their considered legal advice that the Speaker should not accept the amendment. They were ignored.  In answering points of order, the Speaker made clear that had not considered the wider potential effects of his decision.

Why does this matter?  First, because the Speaker’s authority derives from his position as MPs’ elected officer, his adherence to expert advice, and his neutrality.  None of these operated here:  he reached a decision on his own personal authority, he ignored expert advice, and he did so on the substance of the amendment, that is not in any neutral way.

Secondly, the Speaker thereby undermined not just the procedures of the House, but the status of the Clerks—why should any MP or Government seek a ruling as to the correct legal procedure now, when the Speaker may simply decide to change the rules?  Indeed, what IS correct legal procedure, if the Speaker is making decisions as he alone sees fit?

Thirdly, this action was in fact deeply anti-constitutional, and so deeply anti-democratic.  The primary point of our constitution is to allow the passions of politics to be channelled through Parliament.

Parliament may or may not do a good job of it from time to time.  But we undermine Parliament at our peril.