If you are a foundation (level 3) or undergraduate student (level 4, 5 and 6), you can only resit if you have failed the year.
If you are a postgraduate student (level 7), where you have failed a unit, you will be able to resit every failed assessment.
If you have failed one element of assessment, but have passed the unit overall, you will not be entitled to resit the failed unit, unless your programme stipulates that you must pass every element of assessment. (An element of assessment could be an exam, presentation, essay, or any other kind of way that you are assessed within that unit. Some units have multiple elements of assessment - for example, an online quiz and a written report - and all will contribute to your overall grade for that unit).
Please see the Assessment Regulations for more information.
If you feel you have been disadvantaged by circumstances beyond your control and would like to know your options, please follow this link: Assessment Mitigation and Appeals