Islamophobia entered Britain’s political lexicon nearly 30 years ago. Ever since, there have been fierce arguments over whether its definition could threaten free speech. The Runnymede Trust, then chaired by Trevor Phillips, the broadcaster, defined Islamophobia in 1997 as overt and covert hostility – including physical attacks – on Muslims, as well as social exclusion and segregation. If the nature of hatred against Muslims were defined, it was hoped, public bodies, councils and businesses could adopt policies to combat prejudice, discrimination and hostility. Muslims and Islamic advocacy groups sought to establish a standard similar to the definition of anti-Semitism. However,...