Thank you for the considered response Renal - fortunately I managed to handle all the situations I had with relative tact (presumably, as I'm registered now).
It's also something that I think varies a lot between placements. The only examples I can think of particularly are OT/PT based due to the introduction of role-emerging placements and placements with long-arm supervision; my final placement was long-arm supervision in that I got supervision from an OT once a week - the rest of the time I was expected to do group and individual work with long-term MH patients either alone, or with a student nurse if I was lucky (oh, and the trusted pull alarm on my belt).
This included things such as doing individual risk assessments (and documenting) prior to group sessions, to say whether I felt that person X's current signs/symptoms/presentation were compatible with attending safely (for themself/other patients/staff).
I also took the 'discuss with supervisor/uni asap' approach, but still felt that I was being asked to exercise a lot of judgement at times (although obviously I would consult with the nursing team and all handover notes/documentation as well, sometimes the pts key nurse simply hadn't seen them that morning).
The addition of 1st year student nurses as a 2nd 'staff' member in group was in some ways good, but in other ways I had their mentors suggesting that I was responsible for them as well (and did end up debriefing). I still have mixed feelings around that, and am not sure how appropriate it was (medicine were only called in as needed on the unit generally, ditto psychologists).
On other placements I was asked to decide (for example) which transfer assessments I could safely delegate to an assistant technician, and which not. That is a lot simpler, particularly if you discuss a red flag list with your supervisor...but I still think it raises 'when, what, why?' questions in terms of preparation and feeling comfortable enough with your supervisor to be able to say no. (This para is prompted by the thread I was just reading re: mentorship on this board, which saddens me...although I know that some of my colleagues had similar experiences on placement).
When I referred to delegation, I was thinking of a number of scenarios (which I'm comfortable to discuss in open forum as it's 2 years since I was a pre-reg student).
The main one was delegating tasks to an assistant/technician, or leading a group with one. On one of my placements there was some feeling that a third year degree student was the responsible one if something went wrong in group, as opposed to the Band 3/4 member of staff due to professional training. Whilst I could understand some of their arguments to a degree, I can't say I was totally happy with it. Other placements felt that culpability would be down to the student, their supervisor and the 'untrained' (hate that description) staff member.
The same applied to work with other students, and was not a problem when working with peers, but as I think I said above, I had some placements where I was expected to be responsible for 1st year nursing student(s), and their decisions to some degree (at which point I put my foot down and said I was only having one at a time, if at all).