'Flying Lawnmower', 'pathetic attempt'
Oh
niknak. 
You used to be a fan.
Only last year you wrote
"I have the utmost respect for most of your postings ..."
Rest assured I don't for one moment think you changed your opinion when I pointed out the glaring inconsistency between posting (about a pilot jailed for turning up to work over the alcohol limit):
“I sincerely hope that he serves the full sentance, gets the help he needs to accept the gravity of his problem, and never, ever flys again”
when, in the ATC forum literally only a few days earlier, you'd posted (about a fellow ATCO):
"A colleague ... on his way to work today, (3pm start), ….. minor shunt ….. observed by the local plod. He was breathlysed. He'd had a bit to drink yesterday but stopped at around 6pm, had a big meal and solid sleep until 10am, nonetheless, he still registered on the machine as having alcohol in his system, albeit below the legal driving limit. Plod asked his occupation, which he gave without thinking and said Officer immediately and strongly suggested he turned around, went home, and phoned in sick. Thumbs up to Plod. 
"
Not for one moment.
So it's OK to fly underneath a bridge?
No, it's not OK because it would be a breach of Rule 5 - unless the bridge is sufficiently high and the supports sufficiently far apart to allow it to be done without breaching the provisions of Rule 5.
..... pathetic attempt to make the CAA the big bad ogre
Given that the pilot was identified (unfortunately for him), the CAA had no sensible option but to prosecute; it would have been ludicrous if they hadn't. Although I don't entirely share IO540's view, flying under a bridge in breach of Rule 5 certainly falls into his "blatently taking the micky" category.
the pilot was wrong and proved wrong
He wasn't 'proved wrong'; he pleaded Guilty to (admitted) the Rule 5 offence. (NB: Rule 5 does not refer to danger or endangering.)
He did not admit endangering; the CAA did not proceed with that allegation. If they had, my advice would have remained the same: 'Your decision, but IMHO you should plead Not Guilty and challenge the 'endangering.' (I was in a position to call expert opinion evidence that, although illegal under Rule 5, the manoeuvre did not endanger anyone or anything - spoilt for choice of experts actually.)
If you drive across any large bridge when the weather is anything less than perfect you'll notice the effect on the car. etc.
I'm sure, given time to reflect, you can work out the fallacy of comparing the effect of 'less than perfect' weather on a car driving across a large bridge and on an aircraft flying through the air. Or ask a pilot to explain it.
(Just for info, the incident happened on a calm evening with nil or no significant wind.)
..... one wonders if he has the mental capacity to pilot a kite, never mind a powered aircraft.
You're free to wonder whatever you wish.
Personally, I think a pilot with insufficient ability to fly an aircraft the size of a microlight/C150 perfectly safely under a bridge the dimensions of Medway Bridge shouldn't be allowed to fly anything more than a kite.
NB: Just in case you misunderstand me again, I refer to ability; I'm not advocating doing so because it's illegal.
I don't doubt some pilots consider it dangerous. (There was an interesting discussion a few years ago about some pilots who flew light aircraft under a bridge in Scotland. Some strong views were expressed in both directions.) But nor do I doubt there are some pilots who would love to fly under a bridge (depending upon clearance), and are capable of doing so safely, but are deterred only by the risk of being caught.
Just for you, in the hope we can express opposing opinions without personal animosity, my favourite bridge pic:
Safe and legal at about 200 kts.
Considerably smaller than the Medway bridge - but the pilot was considerably more skilled and experienced than most.
FL
(Edit)
englishal
UK courts do not have power to order further training etc.
Of course, there is nothing to stop the CAA coming to such an agreement with a pilot as an alternative to prosecution.
IMHO it would be the far better course in very many, probably most, instances.