applicants for study permits may take part-time or holiday work but must not engage in the following:
* Work for more than 20 hours a week during term time (except in vacation periods), unless it is a work placement and part of a study program and the educational institution agrees.
* Conduct business, be self-employed, or provide services as a professional sports person or entertainer.
* Work full-time in a permanent job.
so you cannot work 40 hrs