This article explains about work placement regulations for Tier 4 students whilst studying in the UK.
Am I eligible to do a work placement as an international (non EU) student?
Tier 4 students can complete a work placement during their studies in the UK. However, there are conditions that must be met:
If the placement meets these conditions, you can work full-time or part-time on a paid or unpaid placement.
Will the time spent doing a placement contribute towards the time I am allowed to study in the UK?
Yes, it will. If you remain on a Tier 4 visa during your work placement, this time will count towards the limit of five years that you may spend studying in the UK.