Possibly advised not to make a big deal about it as to not cause further panic/issues. Suspect the media know more than Joe Public too.
The ex-leader of the EDL took to Twitter to say the crazed attacker had "recently converted to islam" in a tweet which has since been deleted. Says it all really.
At first it was reported as a serious stabbing and not a beheading - hence why an air ambulance was immediately requested.
Also sounds as if the police may well have saved more people being injured by distracting and cornering the attacker whilst taking neighbours to safety, 1 police officer...