If the Commons wants to vote against any Brexit deal that the Government reaches with the EU, it will find a way of doing so.  If it also wants to direct Ministers to then seek to join the EEA, it will be able to do so too.  If it wants to instruct the Government to try to postpone or rescind Article 50, it will be able to do so instead.  Theresa May could of course in such circumstances try to defy MPs, notwithstanding the Fixed Terms Parliament Act, and look to hold a general election.  Or she could resign as Conservative leader, hold the fort in Downing Street for the course of a leadership election, and await the arrival of a Prime Ministerial replacement.

But in the last resort, the Commons has the whip hand – as it would if such an election returned an anti-Brexit or pro-EEA majority to the green benches.  A Government in lieu amendment today implicitly acknowledges that MPs may reject any Brexit deal that May brings back from Brussels, and perhaps attempt to join the EEA or even stop Brexit altogether.  As a Commons Library note makes clear, this amendment grants Parliament “a legally guaranteed veto over the Withdrawal Agreement”.  If it vetoed the agreement, MPs could then do anything they liked, or try to.

The Lords amendment it seeks to replace is different.  As the Library note points out, it also offers the prospect of such a veto, but this would be exercised before any agreement is concluded rather than after it is ratified.  In other words, it creates the conditions for the Commons to take control of the negotiation – to give direction, to borrow the language of the amendment.  Pro-Remain wags will claim that this represents MPs “taking back control”.  But one can’t take back something one has never had: as the note says, this procedure “would be constitutionally unprecedented”.  (Dominic Grieve has tabled an alternative which contains elements of both approaches.)

Under our system, the legislature holds the executive to account.  It does not seek to act as the executive itself.  Britain’s side of the negotiation is confusing enough with Downing Street, four major departments of state, and the best part of 25 ministers trying to run it (plus Olly Robbins, of course).  Chaos would come again were it be placed in the hands of all 650 members of the Commons.

You may ask why Viscount Hailsham, who drew up the amendment, and his supporters in the lower House are proposing this novel procedure.  The answer takes us back to where we started.  They aren’t content to wait until an agreement is ratified before seeking to overturn it – and perhaps attempt to join the EEA instead, or else maybe cancel Brexit altogether.

Rather, as Henry Newman points out on this site today, they want to cramp the Prime Minister’s room for manouevre now.  In particular, they want to head off the possibility of her returning from Brussels with no deal at all.  They are not content to wait.  But it follows that by reducing the odds of no deal, they would thereby weaken May’s negotiating hand, and strengthen the EU’s.

This is the real meaning of the “meaningful” vote.  It is rare for MPs to spurn the chance to boost their own power.  But Conservative ones should recognise that the Hailsham amendment takes them into very deep constitutitional water indeed.  More directly and simply, it also seeks to send the Prime Minister naked into the negotiation chamber.  Up with that they should not put – whatever view they later take of any deal she brings back, if there is one; whatever course they might then decide to pursue.