Sorry, not trying to argue with you, just challenging what the airport may have given as the reason. If anyone gets told by Blackpool that they can't fly in because of commercial heli movements then it's clearly rubbish. But then most of the reasons given by big-headed airports for banning light aircraft are bull****. In this case it's presumably that they decided to buy a cheap insurance policy which transfers all the risk to aircraft operators.
Only other UK airports I know with a stipulated minimum insurance are MoD airfields.
NS