I see that someone has tracked down the Road Traffic Offenders Act reference, which is the one I was thinking of.
The issue of judgement and the law is always contentious, not least because few media reports contain more than 1% of the evidence presented to the court. In my experience, judgements are mostly about right, but given that there are many hundreds of offences judged every day, it's inevitable that there will be the occasional one that looks awry when viewed with perfect hindsight.
Members of the judiciary are only human and the vast majority are unpaid volunteers, albeit carefully selected and trained. I would still rather have a bench decide on an offence like this than trust to the target-focussed judgement of a police officer, who may well be disinclined to take mitigating circumstances into account. As far as I am aware (but I will admit to not have checked this particular variation on a fixed penalty) you retain the right to appeal against it and present your case to the bench.
I would fully expect that, provided you had not endangered anyone and had shown that your behaviour was safe and reasonable in the circumstances, that a fixed penalty might well be overturned.
Of course, I would much prefer it if our courts were not clogged up with such trivia, but that would require common-sense policing. Somehow we have managed to lose this in many places.
As a young lad, my village bobby (who was actually a sergeant) saw his job as preventing crime, encouraging good behaviour and educating youngsters in the process. He once found a friend and myself pushing a stripped down motorcycle along a lane, with the intention of riding around some local woodland (we were about 14). He told us we were breaking the law by pushing it on the road, but went away and came back the next day with a solution. He'd had a chat to a farmer, got permission for us to ride around the edge of one of his fields and had worked out a way of getting our bike there without using roads. He also gave us some useful safety advice and sorted us out with some old crash helmets. He earned the respect of the community and probably prevented (and detected) more real crime as a consequence of his approach.
I doubt that we have many police officers that are allowed to behave like this today, but if we did, perhaps the issue of inappropriate fixed penalties might not arise so often.
Jeremy