The majority of students who graduate in the U.K. will apply under tier 2 of the points-based system. They will need to find a U.K. employer (sponsor) and be sponsored to work in the U.K. If the student prefers to run their own business, their university can endorse their business idea. If they obtain endorsement that their business is innovative, viable and scalable then they can apply for a visa to start their own business.
