I think it important to understand the full context of these so called "anti-extremism" measures. In a speech Mr David Cameron indicated that more must be done by the State to combat extremism. He stated that this extremism was not just of the violent nature but of the NON violent nature as well. He implied the latter was just as dangeorus.
He suggested many of the same tactics used to combat ISIL terrorists such as military strikes along with preemptive arrests, close surveillance and the ability of the Government to take down information on websites they deemed as harmful.
Here is the kicker.
In giving examples of non violent extremism which would lead to arrests, surveillance and the like he SPECIFICALLY claimed that those that questioned the official version of 9/11 or of 7/7 in London as extremists.