You should assume that the technology is pretty reliable.

That's the trouble, everyone assumes that it is (and that is what the authorities rely on), but in fact, it's most likely pretty ropey, what we really need is the AA or RAC of many years back, or another group with the cash to challenge.

Surely these cameras and other devices need calibrating and adjusting for different circumstances, humidity, temperature, pressure etc. what about differing reflective properties, or with a hand-held device, it being moved whilst "locked" onto you?

It's worth finding out if it was a Gatso fixed cam, or a mobile camera. The mobile cameras are calibrated regularly so you haven't got much of a leg to stand on if that's the case. The Gatso cameras are being neglected around the country. Many are broken, many don't have film, and many that are working and have film, haven't been calibrated in a long time. My father recently avoided a speed awareness course after being caught doing 38 in a 30 zone. The camera hadn't been calibrated since 2009 (he was caught in November of last year).