the council are part of the state and so do not have such a right, they should be impartial to differing political groups and their advocates. this isnt a private organisation chosing who to publish, what groups to use their facilities, where i would agree they may have more discretion. they...
so you are agreeing that a council banning a speaker from an event is against free speech. unless the organisation/person is on a proscribed list, council shouldn't involve themselves with who is on the guest list.