If you are studying in the UK on a Student 4 visa you can usually work but with restrictions on the type of work and amount of work you can do. These usually include a maximum of 20 hours (10 hours a week if you are studying a course that is below foundation degree level) a week paid work during semester-time.
It is your responsibility to ensure that your work never compromises your studies nor the conditions of your visa. There are very clear restrictions on working during semester time and the University scrutinises claims/hours of work to ensure compliance. Failure to adhere to the conditions of your visa could have a significant impact upon your ability to continue studying with the University.