Judge each lecturer when you meet them etc. Like where I did my A Levels teachers were meant to allow us to call them by their first names, and most did, but we had one teacher who insisted on Sir.
At university my first contact with almost all - via email - would be sir/miss/prof. Then depending on how they replied to their email I would decide. Like some I kept as prof/sir/miss. But most very quickly it was first name basis. However, there is one prof of mine who I still call prof - even though he's not a prof but a dr. lol. But that is more in fun. One lecturer, our undergraduate dean, I was advised to call him Dr. haha. So yes, it really does depend on the situation.