As of 2004 a blanket law was passed allowing almost no exemptions from jury service. This included police officers, parole officers, and secretarial staff in various courts.
Such people, however, can have significant influence upon a jury unrelated to the facts of the case at hand. I have witnessed this first-hand in a jury where a parole officer was present. The Officer insisted that they knew what guilty people were like because they worked with such people and the defendant of the case was guilty.
The facts of the case had no bearing on the officers opinion, nor did it matter whether or not the crown prosecution service actually proved the case at hand.
Had any other jurist said these lines they would have been ignored.
There are good reasons to keep most everyone in the jury roles, but those whose profession puts them in regular contact with the criminal legal system should ALL be automatically excluded from jury service.
Why is this idea important?
1). A jury should be independent of the enforcement arm of the criminal justice system. Allowing police and officers of the court on to a jury compromises the independence of the jury in the presence of such "experts".
2). An independent jury acts as a check upon the police and the crown prosecution service. If a jury of common sense citizens cannot convict on the evidence the police and crown Prosecution service are sent a powerful signal to improve.
3) The potential for a miscarriage of justice is high when one jurist can be percieved as more familiar or expert in the matters of criminal aprehension or the criminal mind. I have witnessed the effect this can have on one jury first-hand and expect the presence of such an "expert Jurist" can introduce a very severe bias to any jury.