mayorquimby/ haribo: I don't think anyone here is arguing that where race is relevant it shouldn't be taken into account, in for example the case of the Suffolk murders. The point though is that race needs to be relevant to the specific crime committed or which is anticipated to be committed, e.g. that someone reports that they were mugged by a black guy, or in the case of the Suffolk murders that forensic pyschologists believe it to be a white guy. The concern with policing policy and race is, to my mind, two-fold.
Firstly, that there is a general belief that black people are more likely to have committed certain types of crime, and thus it is more likely they will be stopped, searched and potentially arrested on balance for these type of crimes, even if there is no direct evidence for favouring a black person being responsible - their approach to stop and search is pretty clear evidence of this.
Secondly, a more pernicious belief that even absent a specific crime, the behaviour of black people in certain regards may indicate "general" criminal behaviour, e.g. driving a blacked out BMW.
Whilst we all have our personal prejudices and views, the police very clearly have a duty to be impartial and independent in the execution of their duties - see, for example, that they're not allowed to be members of the BNP. Or rather, as Lord Denning said, justice must not only be done "it must be seen to be done".