Postscript 30 October 2015: the Court of Appeal confirmed (rejecting appeal) on 22 October 2015.
Often, progress is assisted by assimilation hence I shall not repeat the excellent review of  EWHC 4165 (Ch) Jong v HSBC by Andy McGregor and Daniel Hemming. (It will be posted here soon, I imagine). Nor indeed will I simply regurgitate how Purle J eloquently dealt with the various jurisdictional issues in the case. Let me instead highlight the main issues:
Plaintiff, Ms Jong, has a contractual dispute with HSBC Monaco SA concerning the proper execution of foreign exchange orders. That the law of Monaco applies does not seem under dispute. HSBC Monaco’s standard terms and conditions, which may or may not apply, contain inter alia a classic unilateral jurisdiction clause: “Any litigation between the client and the bank shall be submitted to the exclusive jurisdiction of the competent Monaco courts at the offices of the bank location where the account is open. Nevertheless the bank reserves the right to take action at the place of the client’s residence or in any other court which would have been competent in the absence of the preceding election of jurisdiction“.
The bank so far has not exercised the clause. (No proceedings are as yet pending in Monaco). Monaco evidently is not covered by the Brussels I Regulation (nor indeed by the Lugano Convention).
Co-defendants are the HSBC Holding and HSBC Private Bank. Ms Jong did have contact with these over the alleged level of service. Perhaps unusually, Ms Jong (or rather, her lawyers) decided to issue proceedings against HSBC Monaco first. The English co-defendants were only added later, quite clearly in an effort to support the exercise of jurisdiction over HSBC Monaco.
The Brussels I-Regulation’s rules on anchor defendants (Article 6; now Article 8 in the recast. Note that the recast does not apply to the case at issue) do not apply to non-EU defendants: whether or not these can be drawn into the procedural bath with the EU defendants, depends therefore on residual national conflicts law. Purle J takes parties and readers through the relevant case-law and holds that while there may be objections to Monaco as a jurisdiction, none of them carries enough weight to override the exclusive choice of court clause.
Of particular note is that Purle J considers (at 26), again with reference to precedent, whether the case against the English defendants may potentially be stayed in favour of having them joined to proceedings in Monaco. (In that precedent, it was suggested that the clear rejection of forum non conveniens in Owusu, may not stand in the way of a stay on ‘sensible case management’ grounds, rather than forum non conveniens grounds). Purle J justifiably hesitates (‘the court must be careful not to evade the impact of Owusu v Jackson through the back door’), before dismissing the suggestion given that no case is as yet pending in Monaco. It is noteworthy that the latter would, incidentally, be a condition for the (strictly choreographed) lis alibi pendens rule of the Brussels I recast to apply (Article 33). I would certainly argue that Owusu and the ECJ’s reasoning behind it, would exclude such recourse to a de facto forum non conveniens rule.