In October this year the Supreme Court heard the appeal in DN (Rwanda) – an important case which will take its place in the line of authority comprising Lumba  UKSC 12 and Kambadzi  UKSC 23. In particular, the Court's judgment will authoritatively determine the circumstances in which a public law error in a prior administrative act or decision will vitiate a subsequent decision to detain, giving rise to a claim for false imprisonment.
For around the past seven years, the general question of when a public law error will render detention unlawful has been answered by reference to the test identified by Lord Dyson in Lumba: namely, whether the error "bore on and was relevant to" the decision to detain. On occasion, the test has been applied in scenarios involving sequential acts or decisions. This is unsurprising given the wide variety of ways in which a decision to detain may be influenced by, or even squarely based on, an earlier executive act. Examples include decisions of the Competent Authority that a person is not a victim of trafficking; Home Office decisions to make or amend policies relating to detention; and decisions that further submissions do not amount to a fresh claim.
DN's case presents an example which is both complex and striking.
DN was a refugee who was found to have lost his protection against refoulement by operation of the Refugee Convention Article 33(2), taken with the Nationality Immigration and Asylum Act 2002, s 72 and the "Specification of Particularly Serious Crimes" Order 2004. Article 33(2) provides that protection against refoulement may not be claimed by a refugee who, "having been convicted by a final judgment of a particularly serious crime, constitutes a danger to the community". Section 72 provided that persons convicted of specified crimes were presumed to meet this description. The 2004 Order did the work of specification, but included a very wide range of offences – including that of facilitating a breach of immigration law by a non-EU citizen, which DN committed by assisting a relative to enter the UK and seek asylum.
Because DN was no longer considered to be protected by the Refugee Convention, the Secretary of State was free to make a deportation order against him. This in turn gave rise to a power of detention pending deportation (the Immigration Act 1971 Sch 3, para 2). But for the operation of the 2004 Order, neither would have been possible. As it was, the lawfulness of the deportation order was specifically upheld by the Upper Tribunal and permission for an onward appeal was refused.
Only later did the Court of Appeal hold that the 2004 Order was ultra vires, as it included a number of offences which were not "particularly serious" and was therefore incompatible with the Refugee Convention.  The question was whether, as a result, DN's detention had been unlawful.
On its face, the answer was simple: the error in the 2004 Order bore on and was relevant to the decision to detain – which could not otherwise have been taken – and the Lumba test was satisfied. However, the Court of Appeal considered itself compelled to a different conclusion by its earlier judgment in R (Draga) v SSHD  EWCA Civ 842. In that case the Court – considering a broadly similar factual matrix – had held that the result produced by Lumba would frustrate the statutory scheme governing appeals against deportation. In the Court's view, that scheme – and the broader principles of finality in litigation and legal certainty – required that the Secretary of State be able to rely on the outcome of the appeals process as determinative of the lawfulness of a deportation order, and to authorise detention on that basis, without the risk of a later challenge giving rise to a claim in false imprisonment. DN's appeal was therefore dismissed on the basis that Draga was binding.
DN's appeal to the Supreme Court rested on the proposition that the decision in Draga had been wrong, as there was nothing in the statutory scheme capable of displacing the straightforward application of the Lumba test. The clearest language was required in order to render detention lawful, and general considerations said to arise from the scheme as a whole could not suffice.
The Secretary of State, for her part, contended not only that the reasoning in Draga was correct, but also that (i) the same result flowed from the 1971 Act, Sch 3 which authorised detention on the making of a deportation order irrespective of that order's lawfulness; and (ii) in any event, the test in Lumba could never be satisfied in a case involving sequential acts – in other words, only a public law error in the decision to detain could render detention unlawful.
Bail for Immigration Detainees ("BID"), intervening by way of written submissions,  highlighted the interplay between the specific context of false imprisonment and the general principles governing sequential decision-making in public law. The starting-point in both cases was that any public law error renders an administrative act a "nullity" with no legal effect – a position only recently reaffirmed by the Supreme Court in Miller No. 2  3 WLR 589 at  (memorably describing the Order in Council based on the Prime Minister's unlawful advice as a "blank piece of paper"). The result in DN's case would be that neither the 2004 Order nor the resulting deportation order could validly authorise detention. Given that the tort of false imprisonment is a constitutional protection of a basic common-law right, departure from this starting-point will be appropriate only where detention was mandated by court order or – subject to the questionable correctness of the reasoning in Percy v Hall  EWCA Civ 1348  – by secondary legislation emanating from a different decision-maker. Neither scenario was relevant in the case of DN, leaving the conclusion reached on application of the Lumba test to stand.
The Supreme Court, then, has been left with a number of important questions to resolve. Does the Lumba test apply, and can it be satisfied, in cases involving sequential acts or decisions? If so, what (If any) are the circumstances under which its result will be displaced by the relevant statutory scheme? And do either the provisions governing detention pending deportation, or those governing the statutory appeals regime, compel this result
Given the practical and principled significance of the issues in play, the answers will be eagerly awaited.
 The parties' submissions ultimately called into question the correctness of three Court of Appeal decisions: Draga (on the key issue under consideration); Percy v Hall (holding that constables who had arrested someone for breach of a by-law later found to be invalid were not liable in false imprisonment); and Ullah  Imm AR 166 (holding that a decision to detain could be vitiated by only a sub-category of public law errors in an underlying decision to report).