First, check that the start date of your new course of studies (as stated on your CAS) is no more than 28 days after the end of your current visa. If the start date is later, you must leave the UK and apply from your home country.
Next, you must currently have Tier 4 (General) student leave for a full-time course sponsored by one of these types of Tier 4 sponsor (see how your sponsor is described on the Register of Tier 4 sponsors):
- a UK recognised body or a body in receipt of public funding as an HEI (higher education institution); or
- an overseas higher education institution and you have been doing a short-term study abroad programme in the UK; or
- an embedded college offering pathway courses (this does not include pre-sessional courses); or
- an independent school
If your Tier 4 sponsor does not meet one of these definitions, or if your current Tier 4 visa was issued for a part-time postgraduate course, you must return to your home country and apply for a new Tier 4 visa from there. If you are unsure, or if your Tier 4 visa has now expired, ask your Tier 4 sponsor for advice.
Alternatively, you must have Tier 2 or Tier 4 (Child) student leave.
Students who have previously been granted Tier 4 (General) student leave must also meet the academic progress requirement, or be exempt from it, in order to apply in the UK. For
information about how the Home Office defines 'academic progress', see the Tier 4 policy guidance.
As long as you apply to extend your Tier 4 leave in the UK prior to the expiry of your current visa, you will be lawfully resident in the UK regardless of the length of time it takes for the Home Office to make a decision on your application.