Tell Mama tells us that it “focus[es] on and use[s] the term 'anti-Muslim prejudice'” primarily because of “the work of the Runnymede Trust on Islamophobia”(which it also deems to be “ground-breaking”).
The Commission on British Muslims and Islamophobia was set up in 1996 by the Runnymede Trust; though this actual report is from 2004.
In terms of the Runnymede Trust and its fight against Islamophobia; it's worth noting that it is self-described as a “left-wing think tank”.
So why “left-wing”?
Take this reason for the Runnymede Trust's Leftism: it doesn't believe that there is such a thing as racism towards whites – full stop!
For example, in 2009 it published a collection of essays which argued that whites “are not descrimated against because they are white”. Well, for a start, there is at least one organisation which discriminates against whites: the Runnymede Trust itself! There are of course many others: such as Unite Against Fascism (UAF), The Guardian, Hope Not Hate, various councils, the BBC, various universities and virtually all Leftist/progressive individuals and groups.
So why this Leftist anti-white racism? Basically it's all down to (Marxist) theory. It has become an article of faith (which most Leftists neither question nor even think about) that whites can only be racists, never the victims of racism.
