I did two trips to Gib when I was at Finningley. Once on basic Nav Training and once on the Nav Refresher course a year or so later. "Mac" was the met man in those days and I don't recall any problems.
Quick Friday flit to Lyneham to top up with fuel, then lunch at Oporto and airways to Gib. Coming back it was into Istres, where the French were drinking wine in the aircrew-feeder, then straight back in airways to Finningley on the Monday.
Seem to recall we used Saccone & Speed (?) for the duty-frees, all handled by a very accommodating co-pilot, then, as it was the last ride in the Domini on the course, we lounged around waiting for our postings . . . . 40 years ago!!
