@AnthonyFStevens It's part of the N Ireland agreement, M&S in GB can ship it to NI but it can't cross the border, despite having an 'open border' between NI and ROI. It's madness but the Brexiteers (and DUP) never thought about how it would work.
Actually, the #Tories realised it was unworkable, but that thoroughly trustworthy bastion of integrity Doris Johnson lied to the #DUP to get the agreement through.
#Brexit was a dirty, grubby "back hander deals in darkened rooms" affair from the outset.