So what they mean is 6m separation but at least 3m clear to stop the spread of fire same as the 3m in the french aire. But the problem is those who never put up an awning or have a car the CC are clearly thinking of caravan/awning/car in their spacing they could have 3m spaces for m/h cheaper if they wanted but they aren't bothered they are a caravan club!! It would be great if we had the choice in the UK sadly we don't.I called it "stupid overcrowding" because (as described in the OP) there were 168 vans on a site meant for 70, nothing to do with UK rules.
I agree about Canterbury - as I said there isn't that much space - but it is controlled so that there are no more vans than spaces.
The spacing required is actually 6 metres, not 9, and is in place as a fire precaution. From the model standards:
There are a number of stories to be found about fire spreading between caravans/motorhomes in storage locations where spacing isn't enforced, and plenty of reports of fire spreading to buildings when caravans are parked close.
I don't think one needs a "regimented restrictive set of rules" but the reality is that legislation is in place and it would be a waste of time to promote aires which may be likely to lead to such legislation being flouted.