If your application is fully prepared, and accompanied by relevant documentary evidence of your circumstances, you may be issued a visa without an interview

The final decision on whether you would require an interview or not will be taken by an Entry Clearance Officer at the British High Commission or Embassy, no one else can make this decision. However, generally students may not require an interview (subject to changes in visa regulations for different countries) if they have:

Travelled to the UK in the last ten years and have evidence of this travel
Travelled to the US, Australia, New Zealand. Canada, Switzerland or Schengen countries within the last five years and have evidence of this travel
Prepaid 100% of their tuition fees and have a receipt to prove it.

If no interview is required, your passport would be returned to the application centre, or couriered to you, within two working days or you may be asked to come and collect it. If however, you are called for an interview, you are likely to get an appointment on the next working day. This might slip during exceptionally busy periods.

The student is likely to be called for an interview if he has

Been refused a visa for the UK or for any other country, unless he has subsequently obtained a visa for that country
Been refused entry to the UK or any other country
Failed to comply with the conditions of entry to the UK, or sought an extension of stay there