“Once a judgment has been handed down or given, there are obvious reasons why the court should hesitate long and hard before making a material alteration to it. These reasons have been rehearsed in the cases to which I have referred and I need not elaborate them further. The cases also acknowledge that there may very occasionally be circumstances in which a judge not only can, but should make a material alteration in the interests of justice. There may for instance be a palpable error in the judgment and an alteration would save the parties the expense of an appeal. On the other hand, reopening contentious matters or permitting one or more of the parties to add to their case or make a new case should rarely be allowed. Any attempt to do this is likely to receive summary rejection in most cases. It will only very rarely be appropriate for parties to attempt to do so. This necessarily means that the court would only be persuaded to do so in exceptional circumstances, but that expression by itself is no more than a relatively uninformative label. It is not profitable to debate what it means in isolation from the facts of a particular case.”