It should be noted that from 22 February 2010 those applying for UK student visas by post at an UK Public Enquiry Office under Tier 4 of the points based system will require a confirmation of acceptance for studies (CAS) from their prospective sponsor.
From 22 February 2010 it will no longer be possible to use a visa letter to apply under the UK Tier 4 visa. You must have a confirmation of acceptance for studies (CAS) from the prospective sponsor. This is the case even if the visa letter was issued before 22 February 2010.
You can continue to use a visa letter for the purposes of applying for a Tier 4 visa until 21 February 2010. You can use a visa letter in this situation even if the course of study starts on or after 22 February 2010.