Hi 2 Sheds,
Well yes, and no! 5km visibility is the minumum for VFR flight in Class D, therefore in less than 5km we would be issuing SVFR clearances. In deteriorating visibility I would expect to be asking pilots what sort of clearance they required when the visibility was indicating 5km, in order that we were using the right form of separation criteria when the visibility actually dropped below 5km. It takes a fair bit of pre-planning when changing from traffic information only to full blown standard separation in a restricted piece of airspace.