The Court of Appeal in Teva UK Ltd & Anor v Novartis AG  EWCA Civ 1617 has reaffirmed the principle that while it is not as such unkosher to petition the English courts subsequently to use the spin-off value of that judgment in other jurisdictions (related in some way to using English courts for discovery purposes), it is not proper for E&W courts to make a declaration solely for the purpose of influencing a decision by a foreign court on an issue governed by the law of that very foreign court (here: Germany).
In the case at issue, the claim involves an Arrow declaration (a declaration that a product, process or use was lacking in novelty or obvious as at the priority date of a patent application) with respect to a German patent (admittedly subject to European law which is largely harmonised with the UK approach).
Per Arnold LJ [51-52]
It is not the function of the courts of England and Wales to provide advisory opinions to foreign courts seised of issues which fall to be determined in accordance with their own laws. The English courts have no special competence to determine such issues. If anything, it is likely that they have less competence than the local courts. It makes no difference that the English court and the foreign court are applying the same basic law. Furthermore, comity requires restraint on the part of the English courts, not (to adopt Floyd LJ’s graphic phrase) jurisdictional imperialism. Otherwise the English courts would be enabling forum shopping.
In saying this, I am assuming that the parties have full and unimpeded access to the foreign court. I recognise that the position might possibly be different if that were not the position; but it is not necessary to consider this further for the purposes of the present case, since there is no suggestion that either of these parties lacks full and unimpeded access to the courts of Germany or Country A.