I'm not at Oxford, but heard a few times from a friend who was pulling his hair out over the way his college handled collections.
He mentioned stuff like failing to be told by anyone that an exam had been made a day earlier and missing it then getting angry e-mails about it etc. As well as that he's described very unsympathetic reactions when he's had to have time off sick.
I suppose some tutors are less understanding than others, from the examples I've heard the treatment of students seems quite bad.
On the plus side, though, collections rarely seem to be used as grounds to take serious action against students. And they also seem to be forgotten pretty quickly (especially when you get onto the real exams). So I wouldn't get upset about it harming your Oxford career etc. as that just won't happen. That doesn't stop them making life uncomfortable though. : /
My advice would be to get them out of the way as quick as is feasible and if you don't perform as well as you had hoped you have a perfectly understandable reason why.