At issue in Skatteforvaltningen (The Danish Customs And Tax Administration) v Solo Capital Partners LLP & Ors  EWHC 974 (Comm) is ‘Dicey Rule 3’ which states that “English courts have no jurisdiction to entertain an action: (1) for the enforcement, either directly or indirectly, of a penal, revenue or other public law of a foreign State; or (2) founded upon an act of state“. The assertion of such claims is an extension of a sovereign power of taxation and, per Lord Keith of Avonholm in Government of India v Taylor  A.C. 491, 511: “an assertion of sovereign authority by one State within the territory of another, as distinct from a patrimonial claim by a foreign sovereign, is (treaty or convention apart) contrary to all concepts of independent sovereignties“.
By its claims, SKAT (Danish customs and excise) seeks the return of amounts it says it was wrongly induced to pay out as tax refunds.
Brussels Ia and Lugano (the latter viz a number of defendants domiciled in Lugano States) feature in the discussion because SKAT argue that  ‘: (i) this is a ‘civil and commercial matter’, not a ‘revenue, customs or administrative matter’, under A1(1) BIa; and (ii) it is therefore not possible to invoke Dicey Rule 3 to dismiss its claims against Brussels-Lugano defendants, because to do so would be to decline to exercise a jurisdiction conferred by the Brussels-Lugano regime otherwise than in accordance with its rules.’
If the argument were upheld, any claims falling within Dicey Rule 3 would proceed against Brussels-Lugano defendants while being dismissed against other defendants.
Dicey Rule 3 is not a jurisdictional rule: it is a substantive rule of English law. Yet SKAT’s argument in my view essentially means that an application of Dicey Rule 3 to the matter, would deprive A1(1) BIa of its effet utile.
Logically the BIa /Lugano argument would have had to have been considered first. Baker J does the opposite (his thinking process, unlike writing up, may of course first have considered the BIa argument) and holds at 120 after thorough consideration of the authorities on Dicey Rule 3, that the rule applies: SKAT’s claims seek indirectly to enforce in E&W, Danish revenue law.
In an interesting Coda at 121 ff, he also considers obiter the argument that, in essence, was that in line with a long public international law history, the cross-border recovery of tax refunds wrongfully procured is seen as or assumed to be a matter of revenue law requiring to be dealt with (if at all) by supranational legal instrument. Refence here is made ia to 1925 League of Nations reports.
Justice Baker starts  the BIa /Lugano argument along familiar lines: need for autonomous interpretation. QRS 1 ApS et al v Frandsen  EWCA Civ 1463 is English authority under the Brussels Convention, and CJEU C-49/12 Sunico (to which both the AG and the CJEU refer in C-73/19 Belgische Staat v Movic BV et al) CJEU authority.
 In Sunico, the CJEU considered claims brought by HMRC alleging missing trader VAT carousel frauds. The substantive claims, for damages at common law for an alleged tortious conspiracy to defraud, were pursued in E&W against defendants domiciled in Denmark. HMRC also brought ancillary proceedings in Denmark to attach assets with a view to enforcing any damages judgment obtained in England. Those Danish proceedings were objected to on the basis that they were a ‘revenue [etc] matter’ excluded from BI.
 The CJEU concluded at -, essentially, that because the claim was framed in tort and not as a claim under a tax law, the proceedings were a ‘civil and commercial matter’ and not a ‘revenue [etc] matter’ for the purpose of Article 1(1) of the Brussels Regulation, so long as “the commissioners were in the same position as a person governed by private law in their action against Sunico and the other non-residents sued in the High Court of Justice” (ibid at ).
At 149 Baker J concedes that the decision of the Court of Appeal in Frandsen was incorrect per Sunico, however then holds that the result would be the same: the classification of proceedings as a ‘civil and commercial matter’ or a ‘revenue [etc] matter’ for the purpose of applying the Brussels-Lugano regime does not touch the question whether Dicey Rule 3 applies so as to defeat the claim. He suggests  a search for the lex causae under Rome II would be largely irrelevant for per A16 Rome II Dicey Rule 3 qualifies as lois de police, and finds support for his view that despite scholarly suggestion (i.a. by prof Briggs), Frandsen must not be displaced, in The Law Debenture Trust Corporation  EWHC 655 (Comm) [and in Andrew Dickinson’s reporting on same], in which the English Act of State doctrine was upheld despite Rome II’s classification of the matter as civil and commercial.
At 165 ff he, somewhat superfluously still considers the more recent CJEU authority of Buak and the aforementioned Movic, and decides at 174 that per BUAK and Movic (on the use of evidence etc.) that SKAT was neither attempting nor able to change the rules of the litigation game, either as to the substantive rules of law that would apply in determining its claims, or as regards the procedural rules applicable in the litigation, or as regards the status or effect of any of the evidence it might deploy or disclose. SKAT was not by this litigation pursuing public law proceedings, in which liabilities are determined as if this were a judicial review of SKAT’s actions, decisions or exercise of public law powers.
Yet that the matters are of a civil and commercial nature, in the end does not matter at all: 
To the extent that SKAT relied on the Brussels-Lugano regime as the basis for this court having jurisdiction over the Brussels-Lugano defendants that have been sued, including it may be for serving proceedings out of the jurisdiction, in my judgment it was right to do so. But its having been entitled to do so did not oust or disapply Dicey Rule 3 in respect of those defendants.
Using prof Dickinson’s words (26-27), there is a dissonance here between Brussels Ia and the applicable law. One that, I would suggest, endangers the effet utile of Brussels Ia. Dicey Rule 3’s character as a substantive rather than a jurisdictional rule, does not to my mind save that.
EU Private International Law, 3rd ed. 2021, para 2.28 ff.