... Although the Senior Tutors committee has now convened and decided that, in the vast majority of cases, it will be a right. The exceptions are when you are already in the academic disciplinary procedure for your college, in which case the prelims are treated as being for their purposes another set of penal collections*, and, depending on your college, cases such as when you plain fail to turn up for your exams with no good reason**
That said, your Senior Tutor *will* pull you in if you fail, and may well try and convince you that it would be better for you to go now, voluntarily, so that you can go through clearing, a process that will not be open to people who resit in September and again fail.
*And you must be given written notice of this fact AND of the mark you must gain in order to remain in college
** In doing so your college will be acting against Senior Tutors' Committee, but unfortunately there is nothing you can do about that, as it is for the university and not individual students to enforce the standardisation requirements.