How can the LA prove that their employee has as you claim :
He's been told some information by another parent or a friend and he's used that information to complain to the OPs employer.
That is their obligation when a individul claims that data held by them has been used by a staff member in "private" capacity.
The LA staff l may take a view point of
"have no interest in this low level nonsense"
Data protection is a legal obligation.
Plus they have a legal obligation to ensure staff welfare the fact that your the LA is washing its hands because it cant drop the client/customer is leaving them open to future legal action.
This
and to think they will have a flow chart of procedures shows complete ignorance of education systems in Scotland.
explains that you dont understand how data protection should be implemented.
Without a documented process the LA have nothing to prove that they are implementing controls. So back when the laws were introduced someone in the LA was given a job of looking at how the law applied to schools. That LA staffer wrote a long complex document on how data was processed in schools and then what controls were needed to comply with the law.
When the LA started dealing with SM impacting on staff and decided to wash their hands they needed to assess what data an individual staff member had access to and issue "guidance" (control of data) about what data the Role has access to and what data the "private citizen" can collect and disclose about a data subject.
Is a private citizen employee telling a third party that someones family member is a client/customer of their employer a problem (data breach) when the client list is proprietary information. Can the employee ever be lawfully sacked by their employer for doing that?