In any case, ADS-B will NOT show every aircraft operating in their area even if they have a survelllance system because none of them show the 'whole' picture of ALL aircraft including those which have no transponder or other electronc gizmo.
AFISOs might be able to access something like FR24 to view a rough 'picture' of local traffic but unless there is a feed of primary radar, you will never get the whole picture and in any case, unless the CAA approve it, they will not be able to use it even as an ATM (Aerodrome Traffic Monitor) .
Area FISOs at Swanwick and Prestwick cannot use any type of surveillance system to provide an ATC service either.