BEagle and
Smujsmith,
Post-retirement, I had 13 years with HM C & E. While not on the Excise side (I was a dreaded VAT Inspector !), it occurs to me that the trick might have been to designate the Spit a "Bonded Warehouse". The beer could then have been lodged in it without payment of duty.
AFAIK, there was nothing in the law to prevent a Bonded Warehouse flying off to France if it wished (I don't think the eventuality had even been considered), and when it got there, presumably only French law would apply.
There was a good old tale about Bonded Warehouses which involved the miraculous conversion of whisky into water (the reverse of the Gospel story), but I'm afraid it would be too far off thread to relate here.
Thanks for the enthralling details of the "beer - run"..... Sudden thought: why not fill the empty barrels with good
vin du pays and return to the UK ? (what the Customs man doesn't see won't hurt him).
Danny.