I need a little clarification in here about the usage of Police cop. Is using a 'Police cop' to define the police personnel grammatically wrong in written English.
'Police cop' used as a noun to denote a police officer would be an example of 'redundancy' (saying or writing the same thing twice - a 'cop' is a police officer, so 'a police cop' means 'a police police officer') like e.g. "navy sailor" or "air force airman" and would not be used by native speakers. However it is not grammatically wrong, just as 'police car' or 'police building' are not 'grammatically' wrong. One way that "police cop" would not be redundant would be if it referred to a specialised police officer whose job was to detect wrongdoing by other police officers. In English usage, redundancy is usually defined as the use of two or more words that say the same thing, but we also use the term to refer to any expression in which a modifier’s meaning is contained in the word it modifies.
It would be very rare that it is right to use this. An example: There is "military police" which handles police situations in the army. You might ask "is this man with the military police" and someone could then answer "no, he is a police cop" to make very clear that he is with the "ordinary" police.
In most cases "police cop" will be very redundant and native speakers wouldn't use the term.