Greetings to department's scientists I have enrolled as a PhD student in one of the UK's universities. I have been received an email containing a list of different professors and secretaries in the department. I am a little worried since I don't know how to greet them and I don't know what to say. Could anyone please help me?
I disagree slightly with SolarMike's answer. The academic hierarchy in the UK is very informal. It is fine to use first names for everyone, be they professor, admin staff or cleaner. A simple "Hi Bob" is fine in emails or in person.

I would argue that it would actually be a bit strange to address someone by their title and last name. If you did so, I expect they would quickly tell you it's fine to address them by first name.