Yes, but students have always been allowed to work full-time (non permanent) when they are not 'in term' - usually means during Christmas, Easter, and summer. However, if you've handed in your dissertation and are not doing any sort of academic study, then obviously you're not 'in term'! The idea of part-time employment DURING term is to keep you focused on your studies. They allow full-time employment OUT of term because then there's no interference with your studies. Post-dissertation time is the same thing as out of term.
Andrea - but to get this letter, you still have to have some kind of results/marks, right? I've been trying to e-mail my department to ask for an expedited process regarding my own degree for this specific reason. I told them I don't need actually GRADES, just something saying I WILL be award the degree. I wonder if they would do this right away, considering I only handed in my dissertation at the very beginning of the month? After all, all I need is a pass for IGS purposes.