Try to avoid a "broad" topic and keep to your syllabus. Researching a specific author or a movement in English literature is a better strategy. Since J.K. Rowling was mentioned, you could examine why a particular author became a success at a specific point in time. You could compare the path to success of two authors like J.K. Rowling and Charles Dickens, so you would examine the publishing industry and the interests of the reading public from two different eras of British literature.
You could speak about English literature in a broad sense: what is literature? What makes a fantastic piece of literature? Who do we think of when we hear 'literature'?
Alternatively, you could focus on a well-known contemporary or classical author, like J.K Rowling or Jane Austen. Talk about their texts, their ideas and their writing styles. How do they create a good story using structure, tension, character etc.?