speed cameras

Hi All, New to the forum so apologise if I am repeating myself. Just had a gantry camera on the m25 flash me as I went through. No variable speed limit on the gantry, but the camera flashed none the less. I wasnt doing 70mph, but I wasnt doing less..... Is this a thing? Are they issuing...

https://www.dailypost.co.uk/news/north-wales-news/average-speed-cameras-installed-notorious-15328278 Surprised it has taken this long, frankly.