Having worked in the British civil service myself, I can tell you that most grades dealing with members of the public are *officers* of some level, for example *administrative officers*, *executive officers*, *higher executive officers* etc. Sometimes they have a specific job title relating to the service they provide, but unless you knew what that was "officer" is a pretty generic term that covers most roles and would be understood.

So you might say:

> I went to a local government office and *spoke with an officer*.