This paper considers the ground of religious belief under anti-discrimination law and argues that it is a spectral ground. While discrimination is proscribed in the same way as other grounds, religious belief is never defined; it merely has to be ‘lawful’, which is also not defined. While the proscription emerged from an official commitment to state secularism, in addition to tolerance and diversity, its permeable character allows mainstream Christianity, neoconservative fundamentalism and other variables to seep into it. An analysis of discrimination complaints shows how this occurs metonymically through proscribed grounds, such as sex, sexuality, ethnicity and race. The phenomenon is most marked post-9/11 through what has come to be known as ‘Islamophobia’. The proscription of religious vilification and incitement to religious hatred, which takes discrimination on the ground of religious belief to a new plane, further reveals the tendency of the spectral ground to absorb prevailing political influences.