The evidence that you need to submit will depend on what your mitigating circumstances are but it has to cover the period you are applying for, be on official headed paper, signed and dated. We do not accept photographic evidence, prescriptions or appointment cards. You can find a list of criteria and evidence accepted under the section titled Mitigating Circumstances Application Criteria on:

https://www.beds.ac.uk/student-support/cant-hand-in-a-piece-of-work-or-sit-an-exam/.