“Where expert evidence has been given and apparently rejected by the jury, it could only be in the rarest of circumstances that the court would permit a repetition, or near repetition of evidence of the same effect by some other expert to provide the basis for a successful appeal. If it were otherwise the trial process would represent no more, or not very much more than what we shall colloquially describe as a ‘dry run’ for one or more of the experts on the basis that, if the evidence failed to attract the jury at trial, an application could be made for the issue to be revisited in this court. That is not the purpose of the court’s jurisdiction to receive evidence on appeal.”