I am sure I have pasted these few paragraphs before but doubters should read them and then they should understand why ATCOs indulge in bottom covering when working IFR v VFR traffic;
Control of VFR Flights
Although in Class D, E, F and G airspace separation standards are not applied, ATC has a responsibility to prevent collisions between known flights and to maintain a safe, orderly and expeditious flow of traffic. This objective is met by passing sufficient traffic information and instructions to assist pilots to see and avoid each other. It is accepted that occasionally when workload is high, the traffic information passed on aircraft in Class F and G airspace may be generic rather than specific.
Instructions issued to VFR flights in Class D airspace are mandatory. These may comprise routeing instructions, visual holding instructions and level restrictions in order to establish a safe, orderly and expeditious flow of traffic and to provide for the
effective management of overall ATC workload.
For example, routeing instructions may be issued which will reduce or eliminate points of conflict with other flights, such as final approach tracks and circuit areas, with a consequent reduction in the workload associated with passing extensive traffic information. Visual Reference Points (VRPs) may be established to assist in the definition of frequently utilised routes and the avoidance of instrument approach and departure tracks.