Yesterday, we wrote that Boris Johnson was vulnerable to a pincer movement on the UK lnternal Market Bill – part of which, the Government said again yesterday, provides for the breaking of international law.

And today, there are what may be the first signs of it – reports of an amendment to give Parliament, not the Government, the final say in triggering the relevant clauses.

This could attract support from former Remainers, those Tory MPs who object in principle to breaking international law, and Brexiteers who prize the role of Parliament.

It is, of course, only the first shot in the procedural skirmishing on the Bill, which will surely see a mass of amendments.  There are at least three developments to watch for.

The first is what Downing Street may do.  Don’t be surprised if “helpful” amendments are tabled by backbenchers that are Government ones in all but name.  Or if Ministers meet their critics halfway (or more).

Second, there is what Keir Starmer will do.  If he takes the view that Labour should stand back and let the Conservatives tear themselves apart, the party may not push against the Bill in the Lords as hard as some suggest.

Third, there is a questionmark about how far those who oppose breaking international law will go.  ConHome is getting mixed reports.  We will see what they do at Third Reading if rebel amendments have not been carried.

Finally, there is the ERG.  On this site today, Bernard Jenkin, Chair of its steering group, writes that as a last resort Parliament should “enact domestic legislation that will nullify the direct effect and direct applicability of the EU laws”.

Number Ten’s position is that this would also breach international law.  By contrast, Martin Howe (and Jenkin) claim that the Government’s own proposals do not break international law.

His argument is that these are justified under that law primarily because the EU’s interpretation of the Northern Ireland Protocol over tariffs threatens the Good Friday Agreement.

Downing Street was pushing the same concern yesterday (despite its different view of the legalities).  Earlier in the week, other sources in Number Ten stressed the need to curb the power of the European Court, UK-wide.

The difficulty for both the Government and the EU is that the Protocol is incoherent, as Roderick Crawford pointed out on this site earlier this week.

It declares that arrangements under the Agreement must “maintain the conditions necessary for continued North-South cooperation, avoid a hard border and protect the 1998 Agreement in all its dimensions”.

The core of the problem is that Unionists and Nationalists in Northern Ireland have different readings of what the Agreement sets out.

To Unionists, tariffs in the Irish Sea would break the consent principle.  To Nationalists, tariffs on the Northern Ireland land border would, by definition, constitute a hard border.

That Boris Johnson is now conceding that an Agreement he signed and lauded, less than a year ago, is nonetheless an Agreement that leaves the UK exposed and vulnerable is humiliating.

Furthermore, the Agreement was the basis of his big general election victory last December – the deal was “oven-ready”, remember?  Parts of it now turn out to be inedible.

But the Prime Minister is not the only one to be left exposed.  The then Cabinet backed him up.  So did Conservative MPs pre-election (the Withdrawal Agreement Bill won at Second Reading).

As Jenkin admits this morning, so did he and his ERG colleagues.  They then stood in the election on the basis of a Tory Manifesto which endorsed it.

And the Agreement was also backed by the massed ranks of the Tory press, this site, most conservative commentators, and the mass of Tory activists who worked for a Johnson victory.

It is just as well that most voters will be more preoccupied by the latest Covid Government clampdown, and the potential effects of the “rule of six” on their Christmas, than with international law.

And that if there is a trade deal, which on balance we still think there will be, this entire row will come to nothing – because the relevant clauses of the UK Internal Market Bill will never be enacted.

None the less, when Brexiteers of such impeccable credentials as Michael Howard and Norman Lamont are tearing into you over international law, you have just a bit of problem.