I reckon they looked at the pictures or an old 'tractor', looked at the speed-stamp.....
shook thier heads at it, and sent some-one out to recalibrate the camera!
Seriousely, they CAN read the number-plates. There was a lot of speculation about this when they first came out, and ever since, from such notions as sticking cling film over the number-plate to smearing it with vasceline, or them having a way to 'enhance' the image by reversal....
On the original cameras, the only 'trick' that we discovered that actually worked was to have a photographic flash-gun and a 'slave cell' trigger in the number plate light, so that when the Gatso camera flashed (and they always flashed originally) the camera flash in the number-plate lamp also flashed and caused the camera to over expose the picture....
These days, they are digital cameras, not halide, and are linked to computers; the camera offers a picture to the puter and optical regognition tries to pick out the number plate automatically, but if it cant, it gets passed to a human handler, and if they cant imedietly pick out the plate, they can go back to the original 'footage' and go through it frame by frame, to get a better image.... they can also do some engahncements on it, and I believe the cameras have Infra-Red and UV filters in them, and they can seperate out the 'layers' to get a clearer image......
Basically, if they want to, they' will do you...... only way they cant, is if the plate is missing or obscured.
But when they get passed to a human handler, they can get quite cunning, and even if they cant get an index from the picture, they look at the make and model, colour ans stuff, and use the DVLA data-base to narrow it down to a number of possible veichles, and see if they get a 'partial match'.
Now, imagine, picture of the back end of a motorbike; how much detail are you going to see?
I'm a biker, and half the time I couldn't tell you from a back end view what make a bike is, let alone model........ but the Met, in a clamp down a couple of years ago, managed to 'nick' a whole bunch of bikers running gatso's with small, obscured or even false number plates......
They used old fasioned detective work, and aparently, they identified a number of bikers from their crash-helmets, the make, model and paint schemes.....
The reality is probably NOT that the number-plate didn't trigger the camera or was unreadable.......
But that the notoriousely unreliable Land-rover speedo, was over reading, and the car WASN'T going that quick.......
Or the camera had the 'trigger' set to a speed above what you were doing...... they dont always set it exactly at the limit, or even +10% add 2..... depending on how many hits they get......
Or some cameras aren't actually 'activated'.....
Or the instance was tagged as a 'marginal' and not worth prosecuting, unless they cought the same number habitually triggering cameras on margin.....