British motorists sometimes warn of a speed-trap by headlamp flash, although it is not legal to do that.
However, they also use a flash to warn of some obstruction or hazard ahead.
It may vary from one Police Force to another, but my local one publishes in advance the roads where its mobile cameras will be operating. Not in detail, just the road name or number.
We still have fixed speed cameras too but whether they still operated, is another matter because the way they were funded changed. Perhaps more common are the Average Speed Cameras operating over distances of some miles.
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SinlessOnslaught Vehicle separation is not a legal matter here but is strongly advised. I don't know, but suppose a tailgater could be charged with "driving without due care and consideration" or even the more serious offence of "dangerous driving".
Some stretches of the motorways have chevrons painted on the surface, with roadside signs telling you to keep a 2-chevron length between your vehicle and that in front. The spacing is presumably calculated to work up to 70mph, the maximum permitted on motorways and dual-carriageways unless signed as lower. Most drivers seem to obey them fairly well.
Though over the last decade or so I have gained the impression that more motorists are quite happy to cruise along the motorways at comfortably within the limit, even as "low" as 60mph. Fine provided they obey the lane rules, and don't hog the middle lane where they could create queues and incite dangerous impatience among drivers wanting to proceed at 70mph.
