Having close ties with Turkey in economic, political and strategic terms, the United Kingdom is the leading European country after Germany where the Gülenist Terror Group (FETÖ) enjoys a strong organizational structure. Due to the high Turkish population in the U.K., the organization could easily meet support and managed to complete its networking activities in a short span of time. Thus, FETÖ established a wide range of networks encompassing educational organizations, dialogue centers, relief organizations, and think tanks in the country. Although various articles, news reports and studies have been published on FETÖ, it was noted that no comprehensive study focusing on FETÖ’s U.K. organizations had been conducted to date. This report aims to fill this lacuna. The report’s primary purpose is to inform the public and decision-makers of both countries about the group’s activities and organizational structure in order to eliminate possible threats FETÖ might pose to Turkey-U.K. relations, which have progressed in a strategic nature particularly after Brexit. The field studies and research conducted on the subject reveal that the British public is not sufficiently informed on FETÖ, which helped the group militants create a false image of the organization and maintain their activities without meeting serious obstacles. Although this report has been written with the intention to inform the public, it also aims to provide motivation in order to expose the true colors of the group in the U.K. It also hopes to put cooperation mechanisms into action to prevent the expansion of the organization’s networks and seeks to contribute to the bilateral relations by presenting a number of recommendations to avert possible future problems between the two countries.