I get what you mean. If you've ever tried doing 70 in lane 3 of a motorway, you feel like a sitting duck. People do way in excess of 70, and it leads to some very aggressive tailgating etc.
Nobody seems to accept that 70 is the limit, people think that the perceived buffer of 10%+1 means that you should drive at that. The natural flow I find is around 80-85ish, depending on how accurately the speedo reads.
The limit really should be 80, but then people would do 90+. I don't think UK drivers can be trusted to have de-restricted roads like Germany, they lane hog too much. People stay the hell out of the fast lane over there, unless they're going fast! Tough one.