I've spotted a few things that could cause reasons why the council say no.
1.) All the things you have said are un-fixed objects this means that they can be stolen or made very unsafe which would ruin insurance.
2.)They aren't all particularly strong either what will you do when they break, throw them out, all the council will see is pallets being broken and thrown into the nearest stream/ wood etc.
If you want them to think about it more seriously you would need to look at it from all angles. For instance, the whole thing will need to be properly safety checked, a skip has not been designed to be stood on the underside of and could collapse therefore it will not pass. A pallet will get moved when you are hopping on it failing the safety test.
It's just a case of looking at it from all angles :blink: