Contacted by head of school regarding an issue - should I be worried? I am a PhD student at a UK university. A small part of my time is taken up by (voluntarily) organizing a monthly seminar series. The seminar is open to all PhD students in my school, and is regularly attended by 30 or so students. I took over this duty in January 2018, before which time there were other student organizers.

Whilst I am an organizer (along with two others) of this seminar, all decisions that we take are checked with a particular senior member of staff - who I will refer to as Prof X. It could be said that Prof X is our organizational "supervisor". They check our posters advertising each seminar, our emails, etc. Very little happens without Prof X's knowledge, if not expressed permission.

As part of the seminar, due to the time of day and its duration, we order a certain amount of pizza to have in a break between talks. The money for this comes out of a particular part of the school's budget. We have always done this, as did the previous organizers. We have never discussed our budget for this pizza, or how much we "can" order. We have always presumed we are within budget, and had no reason to think otherwise. We consider that the amount that we order is entirely reasonable for the number of participants.

I received a surprising email today from my head of school - who I will refer to as Prof Y. This email requested a meeting with all three of us organizers, and explicitly stated that this meeting is due to the fact that our seminar is effectively running over budget, and moreover that this was not approved with them, the budget holder.

This email alarmed me for a few reasons:


Prof Y has, in the past, regularly corresponded with Prof X about matters regarding the seminar, which have then been relayed to us organizers. It is very out of the ordinary for Prof Y to email us directly. Prof Y has in fact never contacted us at all before this email.
Prof X was not CC'd in or BCC'd in to this email. Upon my contacting Prof X about the email, they expressed a great deal of surprise and some concern about the fact that Prof Y contacted us in this way. Prof X did then advise that I should attend the requested meeting.
Whilst we organizers are the ones who request the pizza order, we have no (and have never had any) knowledge of or control over our specific budget. I think it is reasonable to assume that Prof Y knows this, and it is therefore unclear to me what the nature of the discussion at this meeting could be. 
Prof Y is head of department. Perhaps they have disciplinary action in mind, or something of the sort. I have no knowledge of procedures or regulations in this regard, and whether we organizers are liable to face any disciplinary action or on what level.


A further complication is that, outside of the organization of this seminar, Prof X is in fact my own PhD project supervisor - I consider them an excellent supervisor and am on very good terms. I am concerned that developments in this situation could effect this.

My questions are:


Could I be accused of misconduct?
Should I be alarmed about the email from Prof Y? Is it likely/possible that disciplinary action is on the agenda?
During this meeting, how careful should I be? Could I be in danger of serious repercussions here?
I think you should be worried that you and your colleagues might have to go without pizza the rest of the semester if you've already (unknowingly) burned through the budget, and not much else.

You could also worry that in the future you'll have to go through a more formal approval process, which will probably loosen once whoever is involved in the approval gets tired of approving it every week and eventually delegates responsibility again.

To me it sounds like everything you've done is completely reasonable. It's somewhat normal for these sorts of things to fall through the cracks.

If there are any serious consequences that come about from this, then there is some deeper dysfunction in your department that is completely unrelated to anything you've done. There are plenty of things for a PhD student to be anxious about, I'd suggest trying your best to not make this one of them. Just show up to the meeting on time and be apologetic if necessary, and also be understanding.