104 (2) Anything to which this subsection applies shall have the same immunity from—

(d) retention by virtue of a lien,

(d) retention by virtue of a lien,(3) In subsection (2) “relevant power” means any power other than— a power conferred by an enactment relating to customs or excise in its application, by virtue of section 105 or any regulations made under that section, to goods contained in postal packets,

105 (3) Duties (whether of customs or excise) charged on imported goods or other charges payable in respect of postal packets to which this section applies (whether payable to a postal operator or to a foreign administration) may be recovered by the postal operator concerned and in England and Wales and Northern Ireland may be so recovered as a civil debt due to him.

You are reading section 105 as if they have paid the Duty and therefore cannot hold the parcel in lien but:

106. Power to detain postal packets containing contraband.—

(1) A postal operator may— (a) detain any postal packet if he suspects that it may contain relevant goods,

(2) In this section “relevant goods” means—

(a) any goods chargeable with any duty charged on imported goods (whether a customs or an excise duty) which has not been paid or secured, or(a) any goods chargeable with any duty charged on imported goods (whether a customs or an excise duty) which has not been paid or secured,

The Royal Mail has a charter to pay the Duty on our behalf and collect it from us. As there is Duty payable on the item, they are allowed to hold the parcel in lien.You continue to state things but show no evidence - please show your sources or evidence with your statements. Put up or shut up