I do not know of one person sent a ticket on an average speed check camera, I often go a bit quicker than the signage tells me, if the road is clear, no one is working on the roadside and I am not too pissed, not had one yet.
You won't trigger the camera at 80mph, unless they have dropped the speed limit to 50mph or less. You have to really be taking the piss to get caught on the M25 cameras.