I received an NIP for doing 67mph on the M1 at 3.30am at a gantry saying 50mph due to "congestion". I was slowing down but could see down hill ahead that all 4 lanes were clear of traffic. The next gantry showed a return to 70mph. As this seems a case of human error or computer glitch, do I have a case to contest? In addition further down the motorway the gantry was showing my exit lane was closed indicating traffic move to outside lane, however it was clearly open causing another vehicle to swerve from outside lane onto the exit at the last minute.