"The reason for the limited role of the Court of Appeal in custody cases is not that appeals in such cases are subject to special rules, but that there are often two or more possible decisions, any one of which might reasonably be thought to be the best, and any one of which therefore a judge may make without being held to be wrong. In such cases therefore the judge has a discretion and they are cases to which the observations of Asquith L.J., in Bellenden (formerly Satterthwaite) v. Satterthwaite [1948] 1 All E.R. 343 apply. My attention was called to that case by my noble and learned friend Lord Bridge of Harwich, after the hearing in this appeal. That was an appeal against an order for maintenance payable to a divorced wife. Asquith L.J. said, at p. 345: "
"Provided the judge has carefully examined the facts, made appropriate findings in relation to them and applied the welfare check-lists contained in section 1(3) of the 1989 Act and section 1 of the 2002 Act, it is unlikely that this court will be able properly to interfere with the exercise of judicial discretion, particularly in a finely balanced case."
"i) An appeal court should not interfere with the trial judge's conclusions on primary facts unless it is satisfied that he was plainly wrong. ii) The adverb "plainly" does not refer to the degree of confidence felt by the appeal court that it would not have reached the same conclusion as the trial judge. It does not matter, with whatever degree of certainty, that the appeal court considers that it would have reached a different conclusion. What matters is whether the decision under appeal is one that no reasonable judge could have reached. iii) An appeal court is bound, unless there is compelling reason to the contrary, to assume that the trial judge has taken the whole of the evidence into his consideration. The mere fact that a judge does not mention a specific piece of evidence does not mean that he overlooked it. iv) The validity of the findings of fact made by a trial judge is not aptly tested by considering whether the judgment presents a balanced account of the evidence. The trial judge must of course consider all the material evidence (although it need not all be discussed in his judgment). The weight which he gives to it is however pre-eminently a matter for him. v) An appeal court can therefore set aside a judgment on the basis that the judge failed to give the evidence a balanced consideration only if the judge's conclusion was rationally insupportable. vi) Reasons for judgment will always be capable of having been better expressed. An appeal court should not subject a judgment to narrow textual analysis. Nor should it be picked over or construed as though it was a piece of legislation or a contract."