In  EWHC 982 (Comm) Pan Ocean v China-Base Group, Hancock J reviews CJEU authority old and new on Article 25 Brussels I Recast at length, starting with Colzani and Segoura and ending with Profit Sim.
The sole but important focus of the discussion is on Article 25 (1)(a)s ‘in writing or evidenced in writing’ (the Article’s other options for the existence of expression of consent were not under discussion: see at 32).
His conclusion, justifiable in my view, is (at 32) that there is no authority (CJEU or otherwise) which would go so far as to say that agreement to an exclusive jurisdiction clause which was implied solely from the conduct of the parties suffices for the purposes of compliance with Article 25.
At 35 ff he considered obiter the issue of anti-suit aimed at Singapore, had he decided that there is a valid clause, in summary rejecting that, too, at 63.
(Handbook of) EU private international law, 2nd ed. 2016, Chapter 2, Heading 2.2.9, Heading 2.2.9.