Stuff like this has been appearing on Facebook and elsewhere since 2014.

As far as I know, there has been no recent change, though I'm sure that as time goes by more speed cameras are being deployed generally over the UK road network. I don't think there's any evidence they are "set" at 72 mph. A lot of the cameras on the M1 flash even when vehicles pass them going under the limit.

Edited by FP on 09/01/2019 at 08:47

I have already seen M1 gantry cameras flashing since a long time back.

They don't really flash unless you are going at high speed (> 80 MPH but not sure).

Since speedos overestimate speed, you are unlikely to be prosecuted unless over 80 MPH.

Edited by movilogo on 09/01/2019 at 12:53

I normally keep to 70 on motorways and am passed by most other vehicles so if 72 and above triggers the speed cameras they will be raking in a heck of a lot in fines.

It would be surprising if the cameras were set to trigger at 72mph, as ACPO guidelines on speeding thresholds remain at 10% plus 2mph = 79mph

I was under the impression the trigger limit was whatever the local police authority set it to be, some seem to be, as you say, set at limit +10% +2mph (79 on the motorways), others only +5% +2mph (75-76mph). There was talk in the media not that long ago (last year?) about Plod being able to set all limits to 0.1mph above the actual limit.

As usual, we in the UK never do things rationally, e.g. a law states what can and cannot be done, rather leaving it to county councils' police authorities to decide and burying what has been in layers of red tape so very few people know what it is.

I would accept the +0.1mph if many of the camera locations (including mobile units) weren't used as revenue-raising exercises in artificially lower limit zones as opposed to a proven deterrant at accident blackspots where excess speed was the cause. I'd also be more sympathetic if the variable speed limits and those old speed limit matrix signs the small ones) actually worked properly and weren't about 15-30 mins out of date for their restriction/information.

There is still construction and use law that says speedos can be +10% so I think below 77 they will be difficult to make convictions stick if they are contested.

Where on M1 and M25 .. it's highly unlikely all the motorways as different police authorities manage these motorways.

No where - it's not a true thing

"As these posst have been circulating since 2014 an have just re-surfaced I smell a hoax!"

As I said above.

It's either a hoax (if the original intention was to deceive), or an urban myth (if it's just some fake story that has somehow taken root). I suspect the latter.

There is still construction and use law that says speedos can be +10% so I think below 77 they will be difficult to make convictions stick if they are contested.

Speedos are allowed to over-read 10% but not under. If you do a true 77mph then a legal speedo could show 77 to 84, in which case your defence might look a bit thin.