Update 17 01 2023 my article on Articles 33-34 has now been published: Lis Pendens and third states: the origin, DNA and early case-law on Articles 33 and 34 of the Brussels Ia Regulation and its “forum non conveniens-light” rules, The link in the title should give free access to the first 50 takers, and I assume link to the review for those that come after.
In Perform Content Services Ltd v Ness Global Services Ltd  EWCA Civ 981 the Court of Appeal yesterday dismissed the appeal against the High Court judgment which I discussed here.
Two grounds of appeal were at play :
(1) The Court was wrong as a matter of law to interpret Article 33 to mean that jurisdiction was not “based on” domicile by reason of a non-exclusive English court jurisdiction clause that conferred prorogated jurisdiction on the English Court pursuant to Article 25;
(2) The Court was wrong to conclude that a stay was not necessary for the proper administration of justice within the meaning of Article 33(1)(b). The court wrongly failed to place any or any sufficient weight on the fact that the NJ and English proceedings were mirror image proceedings giving rise to the risk of irreconcilable judgments, the core purpose of Article 33 and a core feature of the concept of the administration of justice under the Article. The court wrongly took account of the non-exclusive English court jurisdiction clause and/or an English governing law clause and/or wrongly took account of its assessment that the centre of gravity was Slovakia and/or failed to place any or any sufficient weight on the material connections between the parties and the United States and/or wrongly placed significant reliance on connections between the parties, the dispute and the UK.
On the first issue Flaux C refers ia to UCP and to Citicorp (the latter had not been referred to by the first instance judge, I suggested it could have been), to hold that choice of court under A25 BIa being exclusive or not has no relevance. Like the first instance judge, he rules that A33-34 cannot apply if choice of court has been made in favour of an EU court, exclusive or not.
He then deals obiter, like the judge had done, with the issue whether an A33-34 stay would have been in the interest of the sound administration of justice. He emphasises  the wide catchment area of ‘all the circumstances of the case’ per recital 24, and suggests this must potentially also include the connections which the case has with the EU Member State and indeed the specific court (per the choice of court clause) concerned.
On that he is right. But he is wrong in my view to support Turner J’s analysis at  in Municipio, without any nuance.
Turner J and Flaux C are both right that, the fact itself that the factors which a judge considers in holding that the proper administration of justice does not require a stay, might theoretically have also been relevant in a common law forum non conveniens exercise, does not invalidate the judge’s approach under A33-34. However the problem with the judge’s A33-34 analysis in Municipio is,
Firstly, that it is a case of the tail wagging the dog. The proper administration of justice analysis, exclusively populated by forum non criteria indeed with full reference to that forum non analysis, was put to the front without proper engagement with the substantive conditions for A33-34 to apply at all.
Further, the DNA of A33-34 as I have reported before ( I am preparing an overview for publication), is much, much different from the forum non DNA. By cutting and pasting of the criteria indeed by cross-reference to the forum non criteria without further ado, the A33-34 analysis is irreparably broken. It becomes a case of mixing the blank rounds with the live bullets.
It is worth emphasising that the limited A33-34 analysis are obiter findings only.
European Private International Law, 3rd ed. 2021, 2.539 ff.