APPEAL COURT, HIGH COURT OF JUSTICIARY
Lord Mackay of Drumadoon
Appellant: C Mitchell; Drummond Miller LLP (for Ward & Co, Perth)
Respondent: Erroch AD; Crown Agent
4 June 2013
 On 3 August 2012 the appellant was convicted after trial in the sheriff court on an indictment containing three charges. The first charge was a charge of assaulting a 12 year old boy by making a threat to stab him and robbing the boy of a mobile telephone. The second charge was a charge of assault with intent to rob. The complainers on that charge were a 12 year old girl and two boys aged 11 and 14 years respectively. The offence involved presenting a knife at the three children and demanding that they hand over their mobile telephones. The third charge arose out of the possession of the knife on that occasion and alleged a contravention of section 49(1) of the Criminal Law (Consolidation) (Scotland) Act 1995. The offences took place on the same day - though the first charge preceded in time the second and third by some four hours or so - and they took place at different locations but in the same general area of Perth. The note of appeal is specifically directed to the second and third charges alone.
 By way of brief introduction to the circumstances of the offences, the 12 year old boy to whom charge 1 refers travelled on a bus during which he used his Blackberry brand mobile telephone to listen to music via headphones and to make telephone calls. When he got off the bus he was followed by the appellant; thereafter the threat was made to him and he was in consequence relieved of his mobile telephone. Although the boy was unable to identify the assailant, he gave evidence that the assailant was the man who had left the bus immediately behind him. The appellant was identified as that person by the driver of the bus and from the close circuit television footage taken on the vehicle. Additionally when the police attended at the appellant's house, they recovered the boy's Blackberry.
 As respects the second and third charges on the indictment, the three children were on their way to their respective homes when an adult male, wheeling a bicycle, approached them and asked them the time. In order to answer the inquiry two of the children produced their mobile telephones. Thereupon the adult produced a knife and told them to hand over the telephones. The children ran away, the girl and one of the boys going to a local fish and chip shop. While in the shop the boy observed the adult in question cycle past the shop. An employee in the shop later observed the same cyclist passing by again; he went out and pursued the cyclist and was able to identify the cyclist as being the appellant.
 The first two grounds of appeal relate respectively to (a) the quality of the evidential links dependent on the evidence of the boy who went with the girl to the fish and chip shop and (b) the sheriff's decision to direct the jury that it would be open to the jury to apply what might be termed by way of short-hand among practitioners the "Howden principle" (following Howden v HM Advocate 1994 SCCR 19). The third ground of appeal stems from what happened in the course of the jury trial and challenges the sheriff's decision not to desert the diet pro loco et tempore. It is therefore necessary to set out the two events prompting the motions (for there were two) to desert the diet pro loco et tempore.
 Both matters arose in the examination in chief of a police officer, PC J.S., who, it appears, was the investigating and reporting officer. They are described by the sheriff in his report to this court as "two extremely inadvisable statements made spontaneously by the Constable". The sheriff goes on to say - "Doubtless since he had 20 years' service he ought to have known better and I am also fairly clear that he was doing so deliberately in some misguided desire to assist the prosecution but nevertheless he thought it appropriate to make the statement."
 The first of those statements occurred when the witness was asked by the procurator fiscal depute to view the CCTV footage taken on the bus and whether he could identify the person seen leaving behind the complainer in charge 1. Having pointed to features respecting the clothing of that person (which appear to have been features relied upon by the Crown for its invocation of both the Moorov principle of mutual corroboration and the Howden principle) the officer then said:
"I know him well from the area. Clothing, movement and posture, and I know his movements. It's part of my job to do that sort of thing."
 At that point the solicitor for the appellant moved the court to desert pro loco et tempore on the basis that the officer's remarks disclosed that the appellant was a person with whom the officer had had previous dealings and that the jury might thereby recognise that the appellant had such previous criminal convictions. The sheriff refused the motion at that stage on the basis that what the officer had said did not necessarily involve the inference that the appellant had previous convictions and might be taken as knowledge gained by the officer as a local police officer familiar with the area.
 What happened on the resumption of the officer's evidence is reported by the sheriff thus:
"However not content with causing that difficulty the witness, when he was being asked about an interview which he had conducted with the appellant was asked about the demeanour at the beginning of the interview, replied 'He had an outburst at the beginning, he realised the seriousness of what he had done and that he was arrested for the first robbery. He admitted he was on a bike. His manner was very agitated and on occasions quite aggressive. I have not seen him like that before. He is always quite mild mannered.'"
As the sheriff records, in order not further to draw the attention of the jury to those remarks Mr Holmes, the solicitor for the appellant, very properly postponed the making of a further motion for desertion of the diet pro loco et tempore to the next natural break in the proceedings, namely the conclusion of evidence on the day in question. On the resumption of proceedings the following morning the sheriff refused the second motion for desertion of the diet.
 Having just set out the problem which arose at the trial, it is perhaps convenient to deal with the issues which arise from that at this point, these being the subject of the third ground of appeal.
 In brief summary, counsel for the appellant recognised that this was not a case in which there had been any express breach of the particular statutory prohibition on the disclosure of the previous convictions of an accused person. But, she submitted, that was not truly the test. Rather that test was prejudice to an accused in the suggestion from the police officer that the appellant might have been suspected of earlier crimes or that, generally, he was a person who had dealings with the police and was subject to observation by them in the context of his being a suspected criminal. Reference was made to Pratt v HM Advocate 2000 JC 468. The sheriff set too high a test in asking whether it was certain or likely that the jury would conclude that the appellant had previous convictions or had been interviewed for similar offences in the past. It was sufficient that there be a real possibility that some members of the jury might infer from the officer's remarks that the appellant had previous convictions or was someone who had been involved, in a pejorative sense, with the police in the past. It was an additional, but important, feature that the police officer appeared to the sheriff to have been deliberately acting with a view to aiding the prosecutor; the officer was therefore not in good faith.
 Counsel for the appellant further submitted that even if the sheriff had been entitled not to desert the diet, it was necessary that he give an appropriate direction to the jury to ignore the statements in question. The sheriff had not done that and did not touch upon the matter in his charge to the jury. The jury were thus entitled to pay full regard to the evidence in question and were free to draw inferences from it.
 For his part the advocate depute accepted that the statements made by the police officer were improper and he observed that the sheriff had perhaps treated them kindly. While he also acknowledged that in his report to the court the sheriff did not, in terms, consider the degree and extent of prejudice to the appellant, it could, he submitted, be inferred that he had done so. The assessment of such prejudice was a matter for the sheriff and, it was submitted, the sheriff could not be said to have erred in the exercise of his discretion respecting the assessment of that prejudice and how he should respond to it.
 Whether, having concluded that the diet should not be deserted, the sheriff ought to have given some direction on the matter when he came to charge the jury was very much a matter for his discretion. Reference was made to Fyfe v HM Advocate 1989 JC 138. The sheriff was entitled to take the view which he expressed in paragraph 23 of his initial report that it was better for him to say nothing.
 While we have sympathy for the sheriff in the difficult position in which he was placed by the constable's actions when giving evidence, we have ultimately come to the conclusion that there is force in the contention for the appellant that the diet ought to have been deserted on the making of the second motion to that effect. It appears to us that to judge matters by whether the jury as a whole was "certain" or "likely" to conclude that the appellant had previous convictions or had been interviewed for similar offences in the past may be to state matters too strongly. An accused may suffer prejudice if but one or two members of the jury form the impression from what a police officer says (by way of improper statement) that the accused has previous convictions or is a man whom the police regard as a criminal and have interviewed in that suspect capacity in the past. Further, while we are reluctant to engage in semantics, certainty or likelihood (if by that is meant something more than the balance of probabilities) may also be somewhat overstating the test of whether there may be prejudice to the accused.
 That said, the factor which particularly weighs with us in the present appeal is that the witness was an experienced police officer who, as the sheriff says, ought to have known better. One is not therefore in the situation of an unfortunate, un-elicited remark from a lay witness. The statements which the sheriff recognises were extremely inadvisable came from a witness whom the jury, or at least some of its members, might understandably regard as a witness of some authority and whose credibility was not in doubt. Moreover, as the sheriff reports, it was clear that the officer was deliberately endeavouring to assist the prosecution in a way which was improper. In short, the officer's apparent intention was to convey to the jury an improper message designed to be favourable to the prosecution and thereby prejudicial to the appellant. In our view it is hard to see how one could say with any real confidence that the evidence given by the police constable must, as respects the entirety of the jury, have singularly failed in the constable's apparent intended objective.
 In these circumstances, while we are fully conscious of the discretionary nature of the decision which any trial judge has to take in circumstances in which something of this nature goes wrong in the trial process and prompts a motion to desert pro loco et tempore, with the benefit of the more distant reflection and examination which an appellate court enjoys, we have come ultimately to the view that the proper course was to have deserted the diet.
 Accordingly we consider the third ground of appeal to be well founded. It is thus unnecessary to consider the subsidiary submission that it was incumbent upon the presiding officer to give directions respecting the constable's inadvisable statements.
 It is also in these circumstances unnecessary for us to describe and examine the submissions advanced respecting grounds of appeal one and two, which are superseded by the decision at which we have arrived in respect of the third ground of appeal.
 There is however a further point arising respecting our conclusion that the third ground of appeal is sound and that the trial ought to have been deserted pro loco et tempore on the occasion of the second motion to that effect. In one sense, the third ground of appeal affects all of the charges of which the appellant was convicted since, had the diet been deserted, the trial would have been brought to a halt and matters would have required to have been re-indicted (were the Crown so advised). But the note of appeal is clear in its terms that it is only the convictions of charges 2 and 3 that are under challenge. No challenge is advanced respecting the conviction, and separate sentence, on charge 1. While this matter was aired in the hearing of the appeal, no motion was made by counsel for the appellant to amend the note of appeal to challenge the conviction on charge 1. But, as was observed during the debate before us, there may be cogent practical reasons for which an appellant in a situation such as the present situation might prefer that a potentially all embracing ground of appeal be confined to only some of the charges on the indictment. For clarity, it may be added that the first and second grounds of appeal are entirely related to charges 2 and 3 on the indictment.
 In these circumstances, we shall allow the appeal against conviction by quashing the verdict of the jury whereby the appellant was convicted of charges 2 and 3 on the indictment. There is no separate appeal against sentence and since the sheriff imposed on charges 2 and 3 a sentence consecutive to the sentence which he imposed on charge 1 the quashing of the conviction on the former two sentences does not require us to re-examine the sentence imposed by the sheriff on the latter (charge 1).