Res judicata does not attach to interlocutory orders. It is open to the trial judge, for example, to vary them. So much I knew. Until I read In the Marriage of Bowron (1982) 8 Fam LR 651 (this adventure into the law of evidence is taking me to strange places), I had never thought about whether a ruling as to the admissibility of evidence is final. The answer is, if this case remains good law, that it is not final, even if the result of a voir dire. Justice Baker said:
‘The foregoing reasons raise the question as to whether a court having admitted statements or documents into evidence in the course of a hearing may later in the proceedings reject such document or statement. In R v Watson  2 All ER 293 the appellant appealed against a conviction for burglary and theft on the ground, inter alia, that the trial judge was wrong in law in holding that he had no power to rule on the admissibility of evidence at the end of the prosecution case because he had ruled on it in the trial within a trial, even though there were relevant matters that came to light in the trial that had not done so in the trial within a trial.
In the course of the trial and following a trial within a trial the trial judge ruled that two written statements made by the accused were voluntary statements and admitted them into evidence. From later evidence it appeared however that the statements may not have been voluntary and counsel for the accused submitted to the trial judge that he should reconsider the ruling which he had previously given at the end of the trial within a trial and rejected the statements. The judge refused to reconsider his ruling intimating that the question whether the statements were voluntary had been finally determined in the trial within a trial.
The appeal was heard by the Criminal Division of the Court of Appeal and in the course of its judgment the court said:
“In our view the judge was wrong to rule as he evidently did that he had no power to consider the relevance of evidence, given after the ‘trial within a trial’, on the issue whether the written statements were not voluntary and therefore inadmissible. He should satisfy the judge that the evidence on which he has already ruled is inadmissible the judge must take the appropriate steps to prevent the jury acting on it.
It is the duty of the judge to exclude from the jury’s consideration evidence which is inadmissible. In the case of a written statement, made or signed by the accused, the judge must be satisfied that the prosecution have proved that the contested statement was voluntary, before allowing the jury to decide whether to act on it. Experience has shown that where the question of the voluntary character of a statement has been investigated and decided at a trial within a trial it is only in very rare and unusual cases that further evidence later emerges which may cause the judge to reconsider the question whether he is still satisfied that the statement was voluntary and admissible. But where there is such further evidence the judge has power to consider the relevance of the admissibility of evidence on which he has already ruled.
We are not aware of any English decision directly on the point, but we accept the reasoning expressed in a passage in a judgment of the Northern Ireland Courts-Martial Appeal Court in R v Murphy  NI 138 at 143–144, delivered by Lord MacDermott LCJ, which, though immediately concerned with a question of discretionary exclusion, is equally relevant to exclusion on the ground of legal inadmissibility:
‘Is the discretion spent once it has been exercised against the accused and the evidence has been admitted? We are not aware of any authority on this question, but on general principles we are of opinion that the court’s discretionary powers are not necessarily at an end when the relevant evidence has been admitted. Sometimes the true bearing of evidence said to operate unfairly against an accused person may only appear clearly to do so when seen in the light of evidence adduced at a later stage of the trial and after the material objected to has become part of the record. To say that it is then too late to reconsider the objection would, we think, be to run the risk of letting the technicalities of the situation prevail over the requirements of justice. The admission of a confession as voluntary, on evidence heard in the absence of the jury, may be shown by subsequent evidence to have been clearly involuntary and therefore inadmissible. In such circumstances we consider it would undoubtedly be within the province of the court either to instruct the jury to disregard the evidence as no longer admissible or, in the absence of other evidence capable of sustaining the charge, to direct an acquittal. If this is right, we can see no reason for making a distinction between what becomes inadmissible after being thought admissible and what is seen to be unfair after an earlier view to the contrary. We are, therefore, of opinion that the discretion under discussion may, in certain circumstances, properly be the subject of reconsideration.’
The matter is discussed by Professor Cross in his treatise on Evidence (5th edn, 1979, p 72), in which he refers to R v Murphy:
‘The judge retains his control over the evidence ultimately to be submitted to the jury throughout the trial. Accordingly, if, having admitted a confession as voluntary on evidence given in the absence of the jury, the judge concludes, in the light of subsequent evidence, that the confession was not voluntary, he may either direct the jury to disregard it, or, where there is no other sufficient evidence against the accused, direct an acquittal, or, presumably, direct a new trial.’
We accept the accuracy of this statement of the law.”
Although the latter case deals with admissibility of evidence in criminal proceedings before a judge and jury there is a clear analogy to be drawn in regard to the admissibility of evidence in civil proceedings. If a judge having admitted into evidence a document or statement in the course of civil proceedings, comes to the conclusion later in those proceedings that such evidence is inadmissible then it would in my view be a proper exercise of the judge’s discretion to disregard the evidence and reject the tender.
Suffice it to say, in the context of the present case, that although I have admitted the documents above referred to into evidence at this stage in the proceedings it may well be that such documents in the light of later evidence prove to be inadmissible in which event it might be appropriate in the proper exercise of my discretion to either disregard or reject such evidence.’
I altered the formatting of the quotation a bit to make it easier to read.