An MA or PhD thesis usually constitutes the first academic work of future scholars and it has consequently to follow well-established academic norms. Its content and references must be immediately recognizable and easily traceable by other scholars from all over the world. That is the reason why some organizations developed bibliographical conventions aimed at securing consistency as well as clarity.
The most authoritative reference systems in the UK is the one fixed by the Modern Humanities Research Association (MHRA). Other cultural institutions, such as the MLA in the United States, have created equally important style protocols. British universities tend to adhere to the MHRA guidelines, but you should check with your supervisor(s) if this applies to your discipline. For instance, the MHRA style is not used in the Social Sciences.
In any case, do not forget to comply with the only principle that is shared by all institutions: consistency. Whatever reference system you intend (or are required) to adopt, the feature that decides its effectiveness and functionality is the consistency of all its elements:
Finally, remember that you are supposed to include in your final bibliography not only books and articles but also any audio, video and on-line materials consulted. If these represent a substantial amount, it makes sense to list them separately according to medium.
As an MA or PhD student in Romance studies you will face the difficulty of how to organize bibliographical entries formatted according to different nationally defined style systems. To find out more about how to homogenize or deal with diverging reference styles, click on to: Romance languages and bibliography.