Evidence can be excluded if prejudicial
Do we need further rules of evidence to adequately deal with expert scientific evidence? Evidence can be excluded if it is more prejudicial than probative, on the ultimate issue/hearsay rule, under the common law  and the statutory rules  . Redamayne argues that s.78 of PACE 1984 was not designed for exclusion of expert evidence and that the introduction of an exclusion rule for expert evidence would make it easier to exclude bad science.  Scientific expert evidence will be rejected if it is seen to usurp the role of the jury, for example psychological evidence of witness credibility. Although precedent exists for the admission of certain ‘novel’ scientific expert evidence, the UK courts have a fairly liberal and lax approach which has led to a number of precarious judgments  . One such judgment is R v. kai-Whitewind, in which it allows juries to convict even though the conclusion reached by the expert is indefensible or at the extreme, even wrong.  . One must not forget the indubitable need of expert evidence within our criminal justice system. Importantly, expert evidence is admissible to assist the court with scientific information which is likely to be outside the experience and knowledge of the fact finders. There is no requirement that the expert has to have any special qualifications. An expert in scientific evidence is competent to testify as long as they can provide that they hold believable relevant knowledge and skill, and in the opinion of the judge, he is properly qualified in the relevant field of expertise in hand  . There is no specific rule limiting expert testimony to any particular field and it is often an open field for experts to play upon. The only requirement to be admissible is that such testimony must adhere to certain evidentiary rules which is namely that it is reliable and of relevant to the case. What is of particular concern is that there are no guidelines to assist the trial judge in determination of the “relevance and reliability" of expert evidence. The law on expert admissibility develops on a piece meal fashion and it has been said;-
“English law’s rules of admissibility might induce one to believe that we cannot go on for much longer in this vein, that ‘[s]omething has to give soon" 
It is the strong held believe of many scientists, that science is objective and non-partisan in an attempt to produce information and knowledge that is value free i.e. technocratic advancement.  Our criminal justice system is not based on the same ethos and the use of scientific expert evidence has led to a number of recent miscarriages of justice  , despite much call for reform in this area of the law.  A number of solutions have bee raised such as court-appointed experts, bifurcated trials, having a well educated jury system to the actual of abolition of jury trials in cases were expert evidence is needed. However, each of these solutions also creates further problems and is not always procedurally tangible. For example, the use of court appointed experts is treated with scepticism as it is argued that the jury may pay greater deference to the opinion.  However, despite the many drawbacks expert evidence is still seen as a useful evidential tool along with the other forms of evidence.  Forensic evidence only plays a purposeful role in a small number of criminal cases, it is approximated that expert evidence is used in over a third of contested cases in indicted cases. 
The previous proposals for a judicial gate keeping test were never implemented.  The latest round in the attempt to keep our courts free from ‘junk science’ is proposed in The Law Commission Report (LCR) 2009  . The LCR proposes a new statutory test for determining the admissibility of expert evidence in criminal proceeding’s that applies to evidence proffered by both the defence and the prosecution. There is a clear inequality between the state and the individual as regard resources and finances. At present the burden of proof appears to be upon the defence to challenge expert evidence proffered by the prosecution.  There will be a clear burden of proof on the defence and prosecution wishing to admit the expert evidence. This is a clear improvement in this area of the law. The defence cannot just introduce any scientific evidence; it will need to satisfy the stringent ‘reliable’ test discussed below.
The new admissibility test will replace the present tests of ‘relevance and reliability’. The onus will be on the party adducing the evidence to prove that it is relevant. The first stage of the test will be an enquiry into the expert’s reasoning and methodology to ascertain whether it can be adequately and correctly applied to the facts. Opinion evidence will be seen to reliable if it is ‘sufficiently reliable to be admitted’. A number of factors will need to be shown for this;
(a) the evidence is based on sound principles, assumptions, techniques
(b) those principles, techniques and assumptions have been
properly applied to the facts of the case; and
(c) the evidence is supported by those principles, techniques
and assumptions as applied to the facts of the case.
In determining if the evidence is reliable, the key question the court will inquire whether the theory on which the opinion is based has been and can be ‘tested’. Other important indicators will include ‘margin of error’, ‘peer review’, ‘evidence of impartiality’, “experience and qualifications’ and ‘literature associated with the techniques’. Let’s consider for example peer review, which will undoubtedly include some form of publication, this is not a clear test of reliability. Some recent theories may be of limited scientific value and interest and thus may not receive any official publication. They may still in themselves be a reliable science. Thus, peer review will be relevant but may not be the only factor in deciding if it is sufficiently reliable to be admitted. The list although not exhaustive, needs to be read carefully in order not to exclude a potential useful and relevant scientific development that may aid the fact finders.
It will be at this first stage that the boundaries between the real scientific study and legitimate theory are separated from unsubstantiated claims of shoddy non empirical material, which can be filtered out. If the evidence is found to be reliable then the trial judge would apply the methodology to the facts of the case, in order to work out if the basis is sound. If the theory could not be applied to the facts of the case, it would not be admissible. The final stage of the test is to determine if the expert’s reason is logical in accordance with the methodology that is used. This will ensure that the conclusions reached by the expert must cogently relate to the theory and the substance of the testimony proffered.
These factors are very similar to the factors in Daubert v Merrell Dow Pharmaceuticals, and it will make scientific validity the linchpin of admissibility. However, a major criticism that has been levelled at Daubert  , which may also be seen with these factors, is the difficulty that judges may have in deciding what valid scientific evidence is as non scientists.  Some of the important scientific indicators for the judge to be mindful of may include missing data, a range of values in numerical evaluations, sampling sizes in the scientific evaluation process. Kuhn has shown that even the best quantitative measurements can never provide complete certainty of scientific results.  Courts today are inundated with scientific discoveries and the techniques used to analyse them are increasingly more complicated and unfathomable even amongst other scientists. This will make it difficult for the judge to ascertain that the expert evidence is based on a solid and sound basis and that is relevant to the case.
On the issue of training for judges, the proposals are rather lacking as it does not make training a priority. However, at least it does not propose that the judges will go on a mandatory ‘crash-course’ in order to be able to reach a scientifically well informed conclusion on the evidence presented. Thus, by being less prescriptive in this area it will allow for some room for manoeuvre in the implementation of the proposals. It is argued that that much of the scientific evidence that is used, is infrequently questioned and is only occasionally tested.  If this is the case, then the existing expert evidence, especially techniques such as handwriting, which is often admitted as evidence with no testing or empirical basis, in future may need to be supported with an effective methodology. Intense training of judges in scientific methodology is crucial if these proposals are adopted, due to the complexity and the vast array of scientific information, material and methodology.
In the case that followed Daubert,  it was found that the expert opinion generated from the first hurdle of acceptable methodology, needs to be tested for relevancy and if there are any gaps, then the opinion can be ruled inadmissible.  A similar regime is present within the proposals in which the judge can rule the evidence inadmissible on the same grounds. By focussing on testing of the expert evidence proffered by experts allows us to see the value and limitations of its use  .
In difficult scientific cases the court may employ an independent court assessor. This may raise further problems of bias as it will inevitably be the court that pays the assessor’s wages. Willmore, makes a compelling argument for the use of codes of practice in the use of scientific evidence.  Such codes could provide further guidance to judge’s in measuring and assessing the intricate scientific evidence, by setting further reference points and the weight that should be given to specific evidence presented by experts. The use of codes may introduce further interpretation difficulties. But with the vast array of methodology and techniques that the judge would be expected to grapple with, codes would be of some assistance.
Do the factors listed in the guidelines provide suitable guidance for the trial judge? These proposals are drafted in fairly clear straightforward English. They are logical and coherent and offer a principled three stage test to admissibility. Although this list is flexible and gives the trial judge a great amount of discretion. The subjectivity of the judge’s decision may lead the rules to be interpreted with incredible flexibility as in the Daubert case.  Where does this leave our criminal justice system in the search for a fair test for admissibility? If the rules were applied rigidly, it would be a more demanding requirement than the relevance test. Certain factors may be given less weight, in order to allow for new factors to be considered when it is appropriate. The checklist is a useful benchmark to work from; it focuses the judge’s mind on the important factors, which are salient to criminal trials. As with any other statute, many of the terms will be open to interpretation. It is certain that ‘qualifications’ criterion will certainly exclude bogus qualifications. But do such ‘qualifications’ need to be paper qualifications, or practical experience based?
It has been argued that the Daubert criterion has not solved any of the underlying problems on which courts, experts and others in the criminal justice system operate.  Furthermore, it is arguable if the Daubert test has actually achieved its aim of increasing the amount of useful expert evidence and decreasing the availability of less credible science to then jurors.  No admissibility test will completely ensure that unreliable evidence doesn’t make its way to the fact finders. The design of the rules cannot predict how the judge may interpret and apply them in subsequent cases. Any gate keeping role that we introduce may actually prevent the jury from having access to the latest advances in science, which may later prove to be reliable. This is a major drawback of more rigid admissibility rules, but it adheres to the maxim ‘it’s better to let ten guilty men go free, than convict one innocent man’.
The Court of Appeal expressly rejected a new approach to admissibility, on the basis that there “is no single test which can provide a threshold for admissibility in all cases".  It is argued that the combination of science and law may never be “integrated into a seamless harmony’".  It seems that the ultimate question remains, can we ever produce scientific evidence, that is not prone to some subjectivity and free from value laden judgments? The simple answer is more than likely no. Such a test for the admissibility of expert evidence may be structured in a way that it produces a relationship between law and science that may appear virtuous.  However, they cannot offer a clear answer to how effective the methodology and testing has been applied in a particular case. One must be careful of giving judges more exclusionary discretion, as they may manoeuvre this power to achieve their own subjective political persuasion and needs.  Furthermore, it is argued that many of these exceptions, such as the hearsay rule are ignored by the judiciary and advocates as they may have difficulty in applying this distinction. The new exclusionary rules may be better suited to exclusion of expert evidence in the criminal process because they help focus the mind of the judge on pertinent questions that must be asked of scientific evidence.
There are many criticisms levelled at the present rules on admissibility. Case law and the number of miscarriages of justice show that the present rules are not able to effectively filter forensic evidence. The current rules provide no guidelines to judges on how to use scientific evidence and the exclusionary rules available are used on an ad hoc basis. However, one must not underestimate their effectiveness; they will remain as a further layer of protection if the proposals are adopted. There is no clearly expressed defined burden of proof required of the parties relying upon the use of expert evidence. If the proposals were adopted, it would require a more probing analysis into the quality and credit of the scientific evidence, than is seen by many of the decisions of the cases by courts at the present time.
Many of the problems off admissibility cannot be resolved easily. Many of the untried and untested novel scientific expert evidence would unlikely to pass the more stringent admissibility rules. The new rules will require the expert to show some kind of learning or comprehensive knowledge in a particular field. It must be asked again, would the proposals provide a suitable guidance to judges? Would these clearly defined rules be able to differentiate between science that is able to be defended with logic and justification from other science that is showily attractive, but lacking any real value to the court? This remains to be seen. However, the proposals are much of an improvement to the lax rules on admissibility that we have now.
Analysis of the rules on admissibility should not be carried out in isolation. In order to address the issue of ‘junk science’ and prevent any further miscarriages of justice we need to look at the social, political, and cultural operation of our criminal justice system. Introducing new rules does not guarantee a full proof solution to such a complicated problem. In the US the introduction of the Daubert test may have solved some of the underlying problems of the Frye test. But it also raised further questions on how should the court evaluate the conclusions of evidence that is admissible. As can be seen, for example in the use of DNA evidence, that scientists are in constant battle over statistical probabilities over a probable match. If the scientists cannot agree, then how can a judge? The duty placed upon the trial judge will be highly onerous. It is highly questionable if a legally trained judge would have the ability to grapple effectively with the relevance criterion.
The proposals include many improvements, but the likelihood hat they will become law are remote. Resistance to changes in evidence law by altering procedures or such a virtual tabula rasa in expert testimony may be due to pure self interest of the lawyers.  As a result we will be left with the creaky common law rules of admissibility for the foreseeable future. The new rules apply to science, but will it only apply to the natural science or be widely construed by the judges to incorporate the newer behavioural sciences? This is a question that cannot be answered easily. If the rules were enacted, it would no doubt generate a substantive body of case law, which would in time answer such questions.
The criminal justice system with all its rules and procedures may be seen to put an increasing distrustful arm twisting effect on scientific evidence. The acceptance of systematic errors, degenerate science, the ‘hush hush’ of scientific discovery, unsettled limiting conditions and spurious suppositions may become an anachronism, as experts are called to account under the new rules. There is no ubiquitous solution to the problems associated with the use of expert testimony. Redamayne, concludes; -
“if the state does not test the scientific evidence with which it seeks to convict defendant’s, it should forfeit the right to use it". 
The LCR has provided a fully comprehensive review of the admissibility of expert evidence, from a theoretical perspective. The report is over 90 pages in length, and in such a short report we have only touched on a minority of the points raised. What can be said is that the transformation into practical context would undoubtedly raise many issues of cost, training, procedure. We clearly cannot afford to carry on with the present system for much longer. The report may be a little overly ambitious; as it sates that the changes can be introduced without any significant changes to existing procedures. Without considering changes in other areas of the criminal justice system, miscarriages of justice will continue, as expert evidence is not the only contributor.
The most important conclusion reached by the LCR is that the use of expert evidence requires stricter control and supervision than at present if its forensic potential is to be attained. Putting both the prosecution and defence to proof in order to introduce expert evidence is squarely a major improvement within the law. The effectiveness of the guidelines will only be fruitful, if they are applied with learned knowledge and understanding, even if at least a basic level to the scientific methodology used. This will allow for more stringent scrutiny of expert evidence.