Unfortunately once again Royal Mail legal services have sent me a cheque for the full amount of the small claim. They are quite understandbly, like with bank charges in the early days, scared of this issue going before a court, even one which will have no bearing on other customers other than they may choose to follow a similar course of action.
In summary:
Despite what I have noted as Royal Mail operators writing or speaking, they have confirmed in their court pleadings that you do not have to pay the £8 or £13.50 to have your parcel delivered. They will invoice their portion of their customs fees later. I advise you to pay the actual customs owing.
Several people have taken them to court for this including me twice, and they have paid. Even if they don't charge you, a debt invoice from them for the £8 or £13.50 is sufficient for you to sue them to "cancel" the debt. In reality, it may end up that you are £8 or £13.50 better off since do not under any circumstances pay this fee. There's not a lot you can do about this as otherwise they will send your debt to debt collectors. I am actually still waiting on clarification they have cancelled it. My claim also including telephone call costs to phone their head office and 0845 number to get my parcel delivered.