If you are in the UK with a short term study stamp or a short term study visa, you are NOT allowed to work in the UK.
If you do, you are breaking immigration rules and this can affect your immigration history and possibly your chances of returning to the UK.
Students on a Tier 4 General visa are allowed to work:
a) part-time during term-time (10 hours per week for courses below level 6 and 20 hours per week for courses at level 6 or above);
b) full-time during vacation periods (Easter, Christmas, and during the summer for undergraduate students).
You can also work full time at the end of your course once you receive your results, until the end of your visa (or up to 4 months whichever is shortest).
If you are unsure about your eligibility to work in the UK, contact an International Student Adviser at firstname.lastname@example.org or come to a drop in appointment in Student Services, Level 5, Owen Building.