The reason Royal Mail is considering banning these items is that it believes or at least it's legal advice believe that it is technically in breach of or that it cannot reasonable ensure that it isn't in breach of Section 14(1) of the Firearms (Amendment) Act.
”It is an offence for an auctioneer, carrier or warehouseman
(a) to fail to take reasonable precautions for the safe custody of any firearm or
ammunition which, by virtue of section 9(1) of the principal Act, he or any servant
of his has in his possession without holding a certificate; or
(b) to fail to report forthwith to the police the loss or theft of any such firearm or
ammunition.”
As you are probably aware Parcelforce Worldwide, part of Royal Mail Group, provides a dedicated service for Registered Firearms Dealers.
As for spare parts,it would be impossible to distinguish between what constitutes a spare part and what is simply part of a piecemeal shipment of a firearm waiting to be assembled at the other end.
