Your nationality can dictate whether you need a visa to study in the UK. If you want to find out what the current rules are for those of your nationality, please visit the UK Visas website.
Student Visitor Visa
The 'Special visitor: Student visitor' category can allow you to come to the UK if you are 18 years or above age, and want to enter:
Up to six months to study a short course;
As a visiting student, you must leave the UK on or before the date that your immigration permission ends. The visitor students are not allowed to apply to switch into any other immigration category while still in the UK. If you want to continue studying in the UK after your immigration permission as a student visitor has come to an end, you need to return home and apply for entry clearance as the Tier 4 (General) student, or in another appropriate immigration category Tier 4- Visa Nationals.
For more information please visit the UKCISA website.