In a recent judgment (for which thanks to Criminal Solicitor Dot Net) the Administrative Court has dismissed an appeal based on a technical challenge to a Gatso camera. The key bit of the judgment appears to be:-
We do not accept that the use of this approved device is fundamentally unfair and consequently a breach of a defendant's right to a fair trial. The device makes use of two completely independent types of technology. The primary speed check uses radar and is dependent on the 'Doppler' effect. The device emits a high frequency radio beam along the road. A vehicle approaching the device will reflect some of the signal back to the device. The frequency of the returned signal will be different from that of the transmitted signal and the difference between the two is a function of the speed of the approaching vehicle. The device is able to calculate the speed from the difference in frequency. Thus the primary speed check is wholly independent of the correct working of the clock inside the device. The secondary check is dependent on the clock. Only if the secondary check tallies with the primary check will there be a prosecution. It seems to us that it is not unfair to require the defence to take on trust the correct functioning of the camera at an interval of half a second because, if the camera timing were not correct, it would be an extraordinary coincidence that the result of the two checks, independently carried out, should turn out to be the same.
Elsewhere in the report the driver claims that he did not realise that he was doing 81 mph in a 50 limit (in a van) and that his van wouldn't do 80 anyway. The judges gave his argument the credence that it deserved.
The full judgment is here.