The trouble now is that the labelling of crimes has become political. Thus, those US media which talked of Charleston as a mentally ill white kid, were maybe saying that white supremacist violence doesn't really count, whereas Muslim violence does count, as terrorism*. So the labelling of Charleston as terrorist is a kind of riposte, and also makes the point that white racism is so endemic, that big news organizations are soaked in it, ditto the police, ditto right-wing politicians, and so on.
I don't know whether you can make the same argument in the UK, since we don't have the same background. It's possible that white violence against non-whites is excused, I'm not sure.
*In fact, they may be saying that white supremacist violence isn't actually white supremacist violence, they just know that, you see.