When it comes to synonyms for the phrase "British prep school," several options come to mind. First, some may opt for the term "preparatory school," which encompasses schooling that is geared towards preparing students for secondary education. Another option is "private school," which often denotes a school that requires enrollment fees and is not government-funded. "Boarding school" is also an option, particularly for schools that offer residential facilities for students. Other synonyms may include "independent school," "upper-class school," or "elite school." Ultimately, the term used may vary depending on the specific characteristics and reputation of the school in question.