If any police officer (whether or not they're a special constable) accesses the database without good cause, they'll be committing both a disciplinary offence and a criminal one.
There was a case, a few years ago, where a police inspector used the database to check up on his daughter's boyfriend. That resulted in him being dismissed from the force and prosecuted.
Every time the database is accessed, a log file is created which records the authorisation code entered by the user and details of the files accessed. There is then an audit process which checks that no unauthorised use was made of the database.
In practice, most (if not all) special constables will probably not be granted access rights to the database anyway.
Chris