Going up the Houghton cut, camera was on top of an unmarked Skoda Octavia estate, on the back right corner, angled to view cars overtaking the Skoda. Small black rectangular box with two lenses. Only one fella in it, couldn't see any hidden lights in the grill. As I passed him you could see him looking at his centre console as if to be checking a monitor, I watched him in the mirror and every car that went passed he was doing the same. What was it? Mobile phone checker, tax? And who runs them? Never seen or heard of one before.