Before you can make a Tier 4 Visa application you must obtain a valid Confirmation of Acceptance for Studies (CAS) Statement from International Student Support. The CAS statement will have a unique reference number stated on the form which is stored on the Home Office online database and includes the following information:
Your CAS is used by the Home Office to assess your ability to meet the points required for a Tier 4 visa application.
If you are a current student and your visa is due to expire then you will require a CAS number from International Student Support. If you are a new student or an applicant then you will require a CAS number from Student Administration.