FIS is flight information service. It's one of the services offered by approach control but is also offered by a FIS unit at Scottish Centre. It is NOT a control service and, as the name implies it provides only information. Stuff like regional pressure settings (for altimeters), runways in use and frequencies. It is a non-radar service so traffic information is given only on known traffic and based on pilot position reports and estimates. Scottish information, at least in southern Scotland, is on 119.87.
They control no airspace at all; they just offer information for aircraft flying outside controlled airspace.