Can you swear in GCSE English Creative Writing coursework?

No, you should refrain from using profanity in GCSE English coursework.

When you started at the school, you may have signed a "Code of Conduct" or a "Student's Agreement", which is a legally binding document promising that you will behave at the school and treat others with respect. The document would have covered your use of profanity on the school grounds and in your school work. The document allows the school to suspend or expel unruly students.

Aside from that, it is not very professional to swear in literature. Very, very few of the world's famous authors actually used profanity in their books. It just isn't necessary.
An author will try not to offend their readers, otherwise they could lose a lot of readers and therefore a large portion of their income. Try to remain professional.
Read a few other great books, such as those by Tolkien or Pratchett, to see how they manage to write epic tales without the use of offensive language. Sometimes, some authors use fictional offensive language, particularly in Fantasy Books, as these will not offend anybody in the real world.

You can find some writing tips on this website (click).