When the intended audience is not specified, we need to make a deduction based on a number of factors, including the level of vocabulary of the text and its theme or topic. Considering these issues leads us to infer that Orwell is writing this essay for an educated Englishman. If you examine the kinds of phrases that Orwell uses and the sophisticated vocabulary, it becomes clear that he is not writing for the "common man" necessarily. Also, when we think about his purpose in trying to inform and persuade his audience about the problems inherent within British Colonialism, we can safely conclude that he is addressing a primarily British audience and seeking to share his misgivings about Birtain's involvement in the leadership of others nations.
In conclusion, Orwell is writing to an educated, mainly British audience to share his ideas concerning colonialism and how by being involved in colonial power, Britain is ironically making itself a slave to the expectations that subjugated nations have of their British overlords.