Last week’s Opinion of Advocate General Rantos (successor to Sharpston AG) in C-603/20 PPU SS v MCP is of note for its emphasis on the principle of mutual trust that lies at the foundation of European Private International Law. Brussels IIa is not staple diet for the blog and I shall leave more intense analysis to others. In short, the AG opined that a Member State retains jurisdiction under the Regulation, without limit of time, if a child habitually resident in that Member State was wrongfully removed to, or retained in, a non-Member State where it in due course became habitually resident.
The third country at issue is India, a non-Hague Convention State, as opposed to the UK, now also a third country but a Hague State. Note that in future A97(2) Brussels IIa Recast give clear priority to A13 Hague Convention’s lis alibi pendens rule, in cases where the conditions for that article are fulfilled: see Cusworth DJ today in AA & BB  EWFC 17 at 27).
Of note to the blog is the AG’s emphasis on mutual trust, at 62 ff:
all Member States comply, in principle, with EU law justifies recognising, subject to certain conditions, the jurisdiction of the courts of the Member State to which a child was abducted and where he or she has acquired a habitual residence. By contrast, if a child has been abducted to a non-Member State, the cooperation and mutual trust provided for in EU law cannot apply. Therefore, having regard to the context of Article 10 of Regulation No 2201/2003, there is no justification for accepting the jurisdiction of the courts of that non-Member State, including in the case where the abducted child has acquired his or her habitual residence in the latter State.
and at 84
Regulation No 2201/2003 is based on cooperation and mutual trust between the courts of the Member States, which allows, subject to certain conditions, jurisdiction to be transferred between those courts. Since provision is not made for cooperation and mutual trust in the case of courts of a non-Member State, it appears to me entirely justified and consistent with that regulation for the courts of the Member State in which a child was habitually resident before his or her abduction to a non-Member State to continue to have jurisdiction for an unlimited period of time, with a view to ensuring that the best interests of that child are protected.
With this he dismissed the view of the referring court, that A10 BIIA should be interpreted as having a territorial scope confined to the Member States because otherwise the jurisdiction retained by the Member State of origin would continue to exist indefinitely. In that court’s view, that Member State would thus be in a stronger position jurisdictionally vis-à-vis a non-Member State than a Member State.
EU Private International Law, 3rd ed. 2021, various places (see Index: ‘Mutual Trust’).