Judgment of Mostyn J
However, this executive summary does little justice to the extraordinary judgment of Mostyn J, which in its first 57 paragraphs ranges over the following areas of law:
(1) The extremely narrow ways in which an arbitral award can be challenged under ss 67, 68 and 69, Arbitration Act 199; ie correction, challenge or appeal on a question of law (paras -).
(2) The additional challenges that are available in family law arbitration given the family court's overriding discretion (see s 33A of the Matrimonial Causes Act 1973), and which are not possible in civil arbitration where an award would be final and binding (s 58(1) of the Arbitration Act 1996). These may include a challenge on the basis of a supervening event that invalidates the basis of the award (Barder v Barder (Caluori intervening)  2 FLR 480
, paras -).
(3) Mostyn J concludes that a court may ' ... on the grounds of mistake of supervening event ... refuse to incorporate the arbitral award in its order and instead to make a different order reflecting the new evidence. Outside the heads of correction, challenge or appeal within the 1996 Act ... An assertion that the award was "wrong" or "unjust" will almost never get off the ground'.
(4) A review of the principles in Barder/supervening event cases (paras -).
(5) A consideration of the concept of 'unforseeability', as applied in the law of contract and tort; in particular in the cases of The Wagon Mound (No 2)  1 AC 617 and The Heron II (Czarnikov Ltd v Koufos)  1 AC 350 where Lord Reid contrasted the probability of drawing a diamond card from a well-shuffled pack (ie probability of 1:3) and drawing the nine of diamonds (1:51) (paras -).
(6) At para  Mostyn J returns to the leitmotif
of a number of decisions of Sir James Munby P that the Family Division applies exactly the same law as the other branches of the High Court. Just as issues of beneficial ownership and sham should be considered applying the same principles if heard in the Family or Chancery Division (A v A  2 FLR 467
), so '... "unforseeability" cannot mean one thing in the Queen's Bench Division and another in the Family Division'.
(7) Whether a number of undecided Barder
cases have been wrongly decided because the concept of unforeseeability has been misapplied, eg the recent Court of Appeal decision in Critchell v Critchell  EWCA Civ 436
('... The death of an elderly man cannot be regarded as anything other than foreseeable and unremarkable', paras [41-).
Pausing at this stage, one might question how the judicial pyramid has been inverted so that decisions of the Court of Appeal can be disapproved or disapplied by a High Court judge (see also L v K (Freezing Orders: Principles and Safeguards)  Fam 35). The answer may lie in the application of the concept of 'per incuriam', eg that the superior court had not been fully appraised of all relevant authorities.
(8) Distinguishing the line of Barder cases that related to 'known unknowns', ie '... where at the time of the order a thing is known and assumed but in fact eventuates to an extent that is not expected', which ought (in Mostyn J's view) to more properly be framed as cases of 'mistake' (paras -).
(9) Reviewing the applicable principles of mistake, at para .
Over 20 authorities are referred to within these first 57 paragraphs, together with a handful of academic articles, papers and practice directions. As the proverb relates, mighty oaks from little acorns grow; given that the basic issue before the court in DB v DLJ was whether an arbitral award should be adjusted by £111,746.
The going becomes decidedly easier in from para  of the judgment, where the court turns to the facts of this case and the reasons why the court allowed H's application and rejected W's claim for additional sums. The following reasons can be extracted:
(a) Firstly, the arbitral award of Gavin Smith ('... a thorough, conscientious and clear piece of work') already contained the safety net of an extendable provision for periodical payments. Mr Smith decided not to impose a s 28(1A) bar '... to provide a safety net in case the wife's share [of the business] is substantially less than the current value would suggest and does not meet her needs');
(b) Secondly, in the event that that first ground is not sufficient to dismiss W's claim, the facts relief on did not amount to a supervening event: ' ... The application was pending and although everyone was confident that it would be granted it must have been recognised that it might be refused. To my mind the decision, albeit unwelcome, was eminently foreseeable in the sense described by the House of Lords and the Privy Council in the cases to which I have referred ... Even if the decision was unforeseeable I do not agree that it "invalidated" the arbitrator's decision in circumstances where the scale of the loss ... would reduce the wife's overall share from 45% to 40% ...'
(c) Thirdly, W's alternative case on mistake failed ('I am not satisfied on the evidence that the wife with due diligence could not have discovered that the council might well adopt a much harder line about unauthorised building developments').
By way of drawing together the many threads contained in DB v DLJ:
(i) The decision confirms that only in exceptional cases will court interfere with an arbitral award.
(ii) The circumstances in which a family law arbitral award can be challenged are wider than in a civil arbitration, due in part to the need to seek the family court's approval of most orders.
(iii) The grounds may include a supervening event or mistake but almost entirely will not be allowed on the basis that the tribunal was wrong or its decision is unfair (cf. route of appeal against a court decision).
(iv) The following practice guidance is given:
(a) The Form ARB1 should be modified to clarify the possible routes of challege (para );
(b) Any notice to show cause why an arbitral award should not be made should be issued in the Royal Courts of Justice and heard by a High Court judge (para );
(c) Mostyn J expresses the obiter
view that a Barder
application can be made to the original court and need not be by way of appeal (cf. CS v ACS  EWHC 1005 (Fam)
, para );
Alexander Chandler is a barrister and arbitrator at 1 King's Bench Walk. Follow him on Twitter @familybrief.
A further article on DB v DLJ  EWHC 324 (Fam) by Tony Roe will appear in the March issue of Family Law.