bb21 wrote:IIRC Singh is not a proper surname in Sikh culture (assuming you're Sikh that is) but as real surnames are not normally disclosed to the general public in Western cultures we have accepted them (and Kaur) as surnames.
Sorry I don't think this has issue got to do with "proper surnames" and practices of a specific community. The passport and visa forms expect a name in the first name and last name fields. These names could be your family names/surnames/caste names/your favourite fruit/whatever - as long as it's consistent in all documents.
I would differ slightly and advice you to be consistent with your passport. If possible ask the uni for a new CAS. It's all electronic and presumably can be regenerated at a short notice.