The clerk cannot refuse to include an item on the agenda if it is legal. If the item was presented too late, or had too little background information for the other councillors to understand "the business to be transacted" by this agenda item, the clerk is able to refuse to add it to the agenda but then should include it on the next one. It it is an agenda item that is outside the scope of the council, is illegal etc, then the clerk is in a position to refuse if it would bring the council into disrepute or law breaking.