|"Is this all real? Or has this been happening inside my head?"
The subject of this article is a real-life person, group, company, product, or creative work that has been mentioned "in-universe" in a canon source. The Harry Potter Wiki is written from the perspective that all information presented in canon is true (e.g., Hogwarts really exists), and, as such, details contained in this article may differ from real world facts.
The Great Fire of London was a major conflagration that swept through the central parts of the City of London, on September of 1666. The Muggles are convinced that the Great Fire of London started in a bakery on Pudding Lane, but there is debate among the wizarding community whether it began in the bakery or in the basement of the house next door, where legend has it a young Welsh Green was being kept. 
- J.K. Rowling's Official Site (Mentioned only)