Evidence can only be deemed to be relevant if it is used to prove or disprove a matter that is in issue before the court. The evidence adduced with the intention of causing the jury to disapprove of the defendant is generally inadmissible unless it is properly presented as evidence of bad character to show the propensity of the defendant to a particular kind of crime.Since scientific evidence is a specific area of expertise it is essential that the person giving evidence relating to scientific findings is suitably qualified, and that the evidence can be relied upon in order to secure a conviction. It is not always easy to draw a distinction between a person who is giving an expert opinion as opposed to evidence of fact1. The Criminal Procedure Rules 1998 (CPR) was reformed in order to restrict the usage of expert evidence2. CPR r 35.1 states that ‘expert evidence shall be restricted to that which is reasonably required to resolve the proceedings.’ One of the dangers associated with the reliance of expert opinion is that miscarriages of justice may occur as a direct result. This was evidenced in the case of R v Cannings 3 in which the expert, in this case, concluded that the death of her children had been non-accidental and that the children had not died of natural causes. It later transpired that the expert used in this case that the expert had been the subject of misconduct inquiries and serious non-disclosure of material facts. On appeal, the conviction was quashed on the grounds that the evidence of the expert was unreliable. This case was very similar to R v Clark (no2) 4 in which the evidence of the same expert used in the Cannings case was regarded as reliable, resulting in the conviction of Clark for the murder of her 2 children. Professor Meadow, the expert in these cases was at the time carrying out a government-funded report into the causes of sudden infant death.