On the new 'Smart Motorways' there is built in enforcement via cameras. On those, the speed limit signs are actually speed limits, with the red ring around them.
The ones I was referring to are advisory and look like this [0].
[0] https://www.drivingtesttips.biz/images/motorway-advisory-spe...
I got hit by this a while ago. Was driving down an empty freeway at night and there must have been road works off the side of the road during the day but I didn't see it until the second sign but the speed camera was after the first sign and I got hit with an $800 fine :/
So if the cameras work, we'll have to do exactly what they say or get fined for speeding.