Seloco
I realised, after overcoming my initial incredulity, that your post was intended to be serious. My response, albeit expressed in a tongue in cheek manner (as you correctly suggest), was also intended to make a serious point.
"The results of such a large, albeit soft object falling suddenly on a busy street of traffic would be unfortunate, to say the least."
I agree they could be, but so could be the results of one of the many large flags flying from official buildings detaching and landing across a windscreen of a moving vehicle. Or a vehicle going out of control as a result of a driver suffering a heart attack. The chances of such events happening are relatively slim, but the consequences could easily be terrible.
The greater the likelihood of some event happening and the greater the likelihood of serious injury or death resulting if it does, the greater the effort which should be made to minimise the risk so far as reasonably possible, but only within reason.
eg Should the CAA prohibit single-crew aircraft from flying over built up areas in case the pilot has a heart attack?
No, in my view.
Banner flying is subject to control by the CAA. All my dealings with the Authority over the years makes me confident that a thorough risk assesment must have been made by competent personnel before permission was granted.
If the point in your earlier post was simply that (had this incident actually occurred) it should be recorded for the purpose of statistical analysis then I agree with you. I'm sorry if I misunderstood the thrust of your earlier post but I formed the impression you disapproved of, or were worried about, banner towing being permitted over London and other built up areas.
Notwithstanding that "traffic and pedestrians are controlled and constrained", I consider the likelihood of a stray banner causing injury to people on the ground pales into insignificance compared with the likelihood of them being injured on the road or pavement by negligence or medical incapacity (their own or someone else's) or mechanical failure.
The risk of being injured (directly or indirectly) by a falling banner doesn't concern me in the slightest, particularly when considered in the context of all the other misfortunes which are far more likely to befall me by reason of living in London.
(I freely admit I dislike the increasing spread of 'nanny state' legislation designed to protect us from any sort of risk.)