GLOUCESTERSHIRE Constabulary has had middle lane hoggers in its sights for several years at least.
Electronic messages asking drivers not to "hog" the centre lane were on display above parts of the M5 in January 2011.
It launched the campaign to ease congestion and cut the risk of accidents.
The Highways Agency and the National Traffic Control Centre agreed that the messages would appear on electronic boards, and the slogan "Don't Hog the Middle Lane" was displayed between J10 and J9 northbound and between J11 and 11A southbound.
Inspector Kevin Roseblade said the problem was dangerous because it encouraged undertaking and tailgating.
The Highway Code Rule 264 on motorway driving states: "You should always drive in the left-hand lane when the road ahead is clear. If you are overtaking a number of slower-moving vehicles, you should return to the left-hand lane as soon as you are safely past. Slow-moving or speed-restricted vehicles should always remain in the left-hand lane of the carriageway unless overtaking."
The police say if traffic is heavy and motorists are going faster than nearside lane traffic, it is acceptable to be in the middle lane.