This paper examines the impact that radical right wing populist groups and hard-line Islamist groups have on each other and on political developments in the UK. In the UK, recent years have witnessed an emergence of a number of right-wing populist groups, notably the English Defense League. Such groups frequently see themselves in opposition to fringe conservative Islamist groups such as Islam4UK, a recent offshoot of the defunct Islamist group al-Muhajiroun. How do such fringe groups influence mainstream political discourse and politics through building connections with mainstream parties or moderate-leaning voters? This paper will apply mobilization theory to explain the evolution of these two groups. Through case studies of these two groups and their interaction, this paper shows that right wing populist and Islamist groups have managed to exert a significant influence on national discourse, but their electoral impact has been minor.