“It’s also important for people to know than even when no speed is displayed, meaning the national 70mph limit is in place, the roadside cameras remain in operation to enforce that limit.”
I think the message there is primarily that the cameras are active even when the NSL applies ... as is the case on the M25 and other motorways. Of course they'd like you to believe that you could be ticketed (against ACPO guidelines) for 70.1 mph, but I seriously doubt that would be the case. Motorways are statistically our safest roads so hard to justify tighter limits than apply to GATSOs etc. enforcing the limits on A and B roads.