The trial judgment
That is essentially what her Honour Judge Penna purported to do in the case under appeal. Put at its most basic, what happened was this. The Judge was trying a child abuse case in the family court, and was asked to decide
i) whether the child had been abused
ii) if so, by whom, and
iii) what the consequences should be, in particular in terms of the child being taken into care
It is reasonably standard for the first two of those questions to be dealt with at one hearing, and for the final question to be postponed till later. So at the conclusion of the first hearing, Judge Penna gave a short judgment in which she concluded that the child had been abused, and that the father was the person responsible.
Various consequential orders followed from this judgment, though through administrative oversight the order was not sealed for some months and therefore technically had no effect. One of those orders was that a perfected judgment would be distributed in advance of the next hearing, which indeed it was - and this is where the legal interest in this case begins.
Judge Penna's judgment, as distributed, said that she had "reconsidered the matter carefully" and now thought that it was not possible to be sure that the father was the perpetrator. Rather, the Judge said, it was either the father or the mother (or both). In itself, that is a perfectly normal finding in this kind of case - there is often inadequate evidence to pin down which of two parents cause the abuse. The question is whether the Judge was entitled to change her mind at this stage, and to bring the mother into the frame once she had already given judgment pinning blame solely on the father.
The Court of Appeal
Unsurprisingly, the mother appealed against this decision. The Court of Appeal judgments, given by Thorpe, Rimer and Sedley LJJ, highlight just what a difficult case this is.
Variations on this question have arisen before. For example, it is well established that when a judge distributes a draft judgment, she is entitled to amend and correct it at any time, whether at the request of one of the parties or not, up until the final order is made which gives effect to that judgment (see, for example, Arden LJ in Re T  EWCA Civ 1736, para 50). Moreover, it seems clear that when a family court case is split into several stages, as this one was, those stages need to be seen as part of the same case, and therefore that 'the final order' is the one made at the conclusion of the entire process, not the consequential orders made along the way at the end of each stage (see Munby LJ in Re A and L  EWCA Civ 1205, para 21).
So what of Judge Penna's approach? In Thorpe LJ's view, while the judge technically had the power to change her mind, she should not have done so unless there had been "interim developments [which were] substantial, if not fundamental" to justify her changing her mind (para 44). Agreeing with this point, Sedley LJ put the matter in this way:
"Between [the first hearing and the second], when she reversed her own decision, nothing had changed except the judge's mind. ... But this by itself is not an objective reason why [the] original judgment should not have been right. Hence the need for some exceptional circumstance – something more than a change in the judge's mind – to justify reversal of a judgment. (para 79)Lord Justice Rimer disagreed. He recognised that it would be an exceptional course of action and that a judge did not have "a general licence ... to change his mind as to the fact finding decisions that he has earlier made" (para 68). Indeed, his Lordship thought that at trial judge:
will only have legitimate occasion to exercise [the right to revisit his findings of fact] in the light of a material change of circumstances justifying it, in particular the emergence of new evidence. A judicial change of mind following the renewed consideration of a decision already made would not ordinarily be regarded as the type of circumstance in which it would be open to the judge to make fresh findings. (para 68)However, in this case Rimer LJ thought that Judge Penna was entitled to change her mind: "She was thereby honouring her judicial oath by correcting what she had come to realise was a fundamental error on her part" (para 71). While matters had moved on in consequence of her initial judgment, no party had materially changed their position, and no party was affected in a way that they would not have been had the judge originally reached what turned out to be her final conclusion. Moreover, the Judge could not reasonably have continued with the case "were she required to proceed with it on the basis of a factual substratum that she now believes to be wrong" (para 71).
Rimer LJ went on to criticise the approach of the majority in the Court of Appeal as based on "little more than an appeal to procedural discipline" which ran contrary to the court's obligation to promote the best interests of the child.
To require the judge, or any other judge, to conduct the welfare proceedings on the basis of a false substratum of fact is to require the judge to shut his eyes to the realities and to embrace a fiction. (para 71)
The tension at the heart of this case is extraordinary. On the one hand, the idea that a judgment given on one day can be fundamentally altered the next for no externally apparent reason is unpalatable. It is also important to understand that "procedural discipline" exists for a reason, namely that process is as important to the rule of law and the provision of justice as outcome.
On the other hand, Rimer LJ's point about deciding the future welfare of a child based on what is now believed by the decision-maker to be an erroneous basis can hardly promote the child's interests. In this case, it made little difference because the mother's mental health difficulties meant that the grandparents were to be the main carers of the child. But in another case, a finding of fact that it was Parent A and not Parent B - rather than a finding that it was either Parent A or Parent B - who abused the child could well result in the child being left in Parent B's care. If the Judge has, meanwhile, come to think that, on reflection, it really might have been Parent B who was the abuser, how could the Judge in good conscience allow that outcome?
I do not envy those who must make the decision as to which of these approaches has the better of it, but my inclination is to think that Rimer LJ is right, and that the Judge was not only entitled to change her mind, but in fact required to do so, once she came to the conclusion that her initial judgment was wrong. But what will the Supreme Court say?
UPDATE, 21.1.13: At the conclusion of the Supreme Court hearing today, the Justices announced that the appeal would be allowed, and the revised judgment of HHJ Penna should be used as the basis for the case going forward. Judgment will follow at a later date.