If you cannot sit your exam, there is no need to defer or to deregister, you can simply not show up. However it is good practice to let the relevant department know, so that they understand the situation. You can then register to take the resit in Autumn. There are a very small number of modules where an Autumn resit is not allowed. These are indicated on Course Finder. If you are in one of these modules, you should contact the Department and explain the situation.
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