One application covering multiple sites miles apart? - Public forum - Planning Advisory Service (PAS)

We have a proposal for several signs in various locations (miles apart) across my Authority area. My initial view is that because each one is a separate site and needs separate consideration that they should be submitted under separate applications. However I am trying to find somewhere in the legislation that says this. Is anyone aware if this is set down in anywhere? Or any advice?  The group who are proposing the signs want to spend as little money as possible. Thanks