Whom and why!
May I correct some misconceptions on this thread.
An aerodrome 'Ground' station will not provide a FIS for that is not their purpose.
An Aerodrome Flight Information Service may not provide a service to aircraft other than those operating or who intend to operate within an ATZ. The service is confined to operations within the ATZ and is never a control.
An Air Ground station must not provide a service and the station is not always required to be manned. It is simply a communication device. They are not empowered to provide traffic whereabouts.
A Flight Information Service (such as the London flight Information Service) will provide a FIS when requested, it should never be presumed.
The LARS will provide; FIS, RIS or RAS as appropiate when specifically requested but only subject to controller workload and in the case of RAS only when the flight is being undertaken in accordance with IFR. It is the pilots responsibilty to request the appropiate service they require and the controller will confirm the specific service being provided. Never presume!
In ALL cases it is required for the pilot to state clearly what service they require. The controller may of course offer a particular service but that must be formally agreed with the pilot.
Only those units promulgated to provide a service are obliged to do so and they are paid to do so. It is of course common for other ATC units to provide a service when requested but they must not be relied upon and they remain unpaid for doing so. Being given 'information' does not imply an 'Information Service'!
70% of the RT test is RT planning. You will be given a list of available radio stations from which YOU select the appropiate unit for each part of the flight. You may only contact a unit that promulgates or has within its structure the obligation to provide a particular service.