Sorry Cass ^^ I think you are wrong there. GATSOs use radar to measure your speed and then triggers the camera and flash to take two photos. The road markings are there as a backup to check that you had travelled a certain distance in the time between the two photos so they and you can check that you were speeding. This does of course rely on the fact that the time between the two photos is accurately known.
AS for the original post: the points are active for 3 years and may be removed from your licence after 4 years.