Students entering university under the age of 18 are still legally classified as children in the UK. Due to this fact, most universities in the UK demand that international students under 18 obtain a UK-based guardian, who acts on the student’s behalf in the event of an emergency.
Emergencies can include dealings with UK authorities, or in the case of a medical emergency, when the student is unable to make a decision for themselves.
Visa applications are also usually dependent on the nomination of a guardian based here in the UK.