Current students can request official documents via the  My Imperial app and full information/guidance on the process can be found on the link below.  The Department cannot provide these documents and if you have any queries please contact the Student Hub.
https://www.imperial.ac.uk/student-records-and-data/for-current-students/request-an-official-document/

Alumni offical document requests/information can be found here, please note that the Department cannot provide these documents.