In reality, the speed limit hasn't been 70mph for years.
Most traffic coppers seem quite happy to let you drive along at 80 - 85 as long as the road / traffic conditions allow.
Anymore then that and you tend to get a evil stare as they pull alone side of you.
Raising it to 80 will just mean that the drivers out there who can barely drive at 70mph safely for whatever reason will feel that they have to increase there speed even further which will cause further accidents.
Keep it at 70 for me, get rid of all fixed camera's and get more coppers on the road with the mandate of ............ If you have our boot down but are driving in a responsible and safe manor then a little stare should be all that is needed to keep drivers in check BUT if your driving like a complete cock then you should be banned from the road and given a rather good kicking

Speed does not kill, dickhead drivers do