Honestly, these Highway Maintenance vehicles are a menace. Every. Single. One. Bastards.
They come screaming up behind you, whizz round you and then pull in front of you and slow down to 61mph. Eventually, you overtake them, get a fair distance in front and the process is repeated.
Many sections of the M25 I drive (Reigate to the M4) have speed cameras which may, or may not work. I'm not risking a fine + points, so I may occasionally drift North of 70 in between these parts. Inevitably, if I am in the "fast" lane and a Highway Maintenance vehicle is on the inside catching a slower moving vehicle it is not M-S-M (mirror, signal, manoeuvre) it is SM. With no gap. Indicator on, instantly pull across even though you've nearly taken my front end clean off.
Complete shitgoblins.