Immigration to UK and visa applications are managed by the UKBA - the UK Border Agency, which is part of the UK Government’s Home office. It is advisable to apply well ahead of time for a student visa. There are a number of different options of student visa available:
Tier 4 (Child) student visa:
is applicable if you are between 4 and 17 years old.
Tier 4 (General) student visa:
You can apply for a Tier 4 (General) student visa to study in the UK if you’re 16 or older, and you have gained admission to a course. Your education provider will send you a confirmation of acceptance for studies (CAS), which must be entered on your visa application.
You will also need to be able to speak, read, write and understand English and show evidence of adequate funds to support yourself and pay for your course.
You should be from a country outside the EEA or Switzerland and will need to meet the other current eligibility requirements (check this link).
You should apply for a visa 3 months before the start date of the course. As part of your application, a healthcare surcharge will also have to be paid.
If your course lasts 6 months or less, you can arrive in the UK upto 1 week before your course starts. If you have enrolled for a longer course, then you can arrive in the UK upto 1 month before your course starts. The length of your stay depends on the course you’re doing and what study you’ve already completed. You can apply to extend your stay, based on your circumstances. You may be allowed to bring in family members or dependents.
Read more at this link: https://www.gov.uk/tier-4-general-visa. The entire guide can be downloaded and printed for your reference, at this link: https://www.gov.uk/tier-4-general-visa/print