Bert - The law states that they can delay the item until the Duty is paid. Check sections 105 and 106.

The points we are making are:

1) The item is held in lien for the handling fee, even if the Duty is offered to be paid.

2) By doing so they are not allowing a customer to dispute the handling charge, which contravenes the relevant sections regarding recompense by 'civil means', and Consumer Law.