Does anyone have any insight into how much 'ownership' of a PhD topic the student can expect if you work on a pre-determined project? I've been having discussions with some of my peers here and none of us are sure how it's meant to work as our supervisors all treat the situation very differently, i.e. some supervisors pretty much claim ownership of all the data the student generates and expect to feature in any publications linked to the project purely because it started with their idea (which seems a little opportunistic), while other supervisors have completely passed all ownership to the student (which seems overly generous). Is it purely down to how your sup wants to play it or are there actually 'rules' for this sort of thing? Anyone know?

I don't think there's anything unusual or too unethical with sups expecting their names on papers their students produce whilst under their supervision. The issue is then if they push for first place without their contribution warranting it, which is a dick move. Like many things in this environment, there's no set of rules, but the rule should really be that the authorship is weighted relative to the contribution.

I can only give my opinion as I don't think there are any set rules. I would say that if you did the majority of the work after your supervisor's idea then you should get first author and they get second on a resulting paper. After all, you probably know the ins and outs better anyway and you did most if not all the work, BUT it was their idea and so the work would never have been done if they didn't think of it, so they get second author on the papers.

I think older sups who have nothing to prove would be more likely to say that the student can take credit, whereas a younger supervisor may still want to be making their own mark in the field and so will want to keep a lot of the credit for themselves. Obviously this is a massive generalisation.

I think first author student, second author supervisor is quite normal if the student did the vast majority of the work, but the supervisor reviewed/critiqued it and offered advice. You might want to consider where your funding is coming from too. It helps if the person who secured the money to allow you the time to produce the work is somehow credited, whether that is authorship somewhere down the pecking order is down to you.