The concerns of the organisers of this event are not primarily security because the CST is not seen at much larger local gatherings. Their concerns are animal rights activists and local authority inspectors who, rightly or wrongly, have in the past targeted this practice. In the USA there have been demos and concern has been expressed in this country too. Even within Judaism there are respectable views against Kapores with the Shulchan Aruch (in a 1565 edition) calling it a munhag shtus and that one should refrain from the tradition. Of course, if the ritual is carried out humanely there should be no reasons to fall foul of the authorities.
So why is CST securing this event? Their role as expressed on their website is :
to protect [the Jewish Community's] many achievements from the external threats of bigotry, antisemitism and terrorism.Does this include preventing legitimate protest albeit, to some, of an inconvenient and unpleasant nature? Unless it is the CST's view that any opposition to anything done by Jews is by definition anti-Semitic the CST should have no truck with this particular event.