But what do the police of the police ?
If what you are trying to say is, who police the police, in the UK there is two authorities who are suppose to do this. Our local elected Police commissioner who are suppose to deal with complaints and bring the public concerns to the police chief and local officers.
An then there Independent Police Complaints Commission (IPCC) who investigate complaints about the police.
That in addition to parliamentary investigations, people suing the police in the courts, and public enquiries. Coroners investigations.
An organisation like the Information Commissioner who investigate police around how they hold data.
There are other commissioners empowered by parliament and home office who keep a eye on other aspects of the police forces in the UK.