Update 4 June 2020 see 1 Chancery Lane’s Richard Collier and Mike Hagan’s paper here, focusing on determination of quantum by foreign (legal) experts.
Update 5 April 2019 see also application in  EWHC 801 (QB) Joshua Folkes v Generali Assurances.
As readers will be aware, the Rome II Regulation on the law applicable to non-contractual obligations, harmonises Member States’ governing law rules on non-contractual obligations (not entirely accurately known in short as ‘tort’). Article 15 clarifies that the scope of the law applicable is very wide:
Scope of the law applicable
The law applicable to non-contractual obligations under this Regulation shall govern in particular:
(a) the basis and extent of liability, including the determination of persons who may be held liable for acts performed by them;
(b) the grounds for exemption from liability, any limitation of liability and any division of liability;
(c) the existence, the nature and the assessment of damage or the remedy claimed;
(d) within the limits of powers conferred on the court by its procedural law, the measures which a court may take to prevent or terminate injury or damage or to ensure the provision of compensation;
(e) the question whether a right to claim damages or a remedy may be transferred, including by inheritance;
(f) persons entitled to compensation for damage sustained personally;
(g) liability for the acts of another person;
(h) the manner in which an obligation may be extinguished and rules of prescription and limitation, including rules relating to the commencement, interruption and suspension of a period of prescription or limitation.
The provision is important, because jurisdictions may differ quite substantially as to which parts of the dispute they consider to relate to the substantive matter of ‘tort’, as opposed to procedural law. Procedural matters are governed by the lex fori and continue to be so under the Rome II Regulation: Article 1(3) provides specifically
‘This Regulation shall not apply to evidence and procedure, without prejudice to Articles 21 and 22.’
Article 15 clearly has a limiting effect on Article 1(3), given that it qualifies a number of issues as being substantive law, even though national law may have considered these to be procedural.
Despite the clarification in the Regulation, combined with the EC proposal and with the recitals, difficulties do of course remain. However in particular ‘assessment of damage’ under Article 15(c) has a very wide scope indeed. For instance the scope of the applicable law arguably includes the determination of whether damages need to be determined ‘net’, taking into account subsequent history which impacts upon the dependency of the party that is being compensated, or rather ‘gross’, at the moment of death: see Cox v Ergo Versicherung, ( EWHC 2806 (QB)] and  EWCA Civ 1001].
In Wall v Mutuelle De Poitiers Assurances, following a severe road accident, plaintiff sued the insurance company in the UK – jurisdictional issues were not under discussion. The Court of Appeal had to review the extent to which French law, the lex causae, had to be applied by the English Courts: utterly and totally, with all its practical implications? Or with due regard for the distinction which the Regulation continues to make between procedure and substance? Tugendhat J unsurprisingly opted for the latter – much more eloquently than this posting can do justice: an English court must not strive to reach the same result as a French court would, let alone insist that evidence given to the English court be in the form of a French-style expert report (no more indeed than a French court would in the reverse hypothesis). As Tugendhat J summarises at 16, in fine: “Rules” as to the assessment of damages are therefore to be “imported”; if there is a rule as to what kind of loss is recoverable, that rule is to be imported. But mere methods of proving recoverable loss are not to be imported.
With reference to Dworkin no less on soft law, the Court did hold that applicable law should be understood to include “judicial conventions and practices”, for example “particular tariffs, guidelines or formulae” used by judges in the calculation of damages under the applicable law: in France, these are the so-called Dintilhac Headings.
Dworkin at the Court of Appeal: that was bound to catch my interest.