The £5million liability IS NOT a requirement in order to land at Blackpool.
It is simply a guidline set down by the insurance company.
The onus for the limit of cover is completely on the operator.
The liabilty you face would be the same at any Airport which would be for the worse case scenario i.e. you fly into the passenger Terminal.
Blackpool is merely being prudent in advising this as a guidline but they obviously won't ask to see your insurance documents or indeed stop you landing if you haven't got £5m cover.
So Smith don't be put off and enjoy Blackpool !