Talkdownman,
You're bang on. My spotting days were from 1970 to 1974 at EGNX. back then, I think it was called Upper Amber 39. One Sunday afternoon we 'potted' both a Sabena and Swissair 747-100 on that very airway. HB-IGA and OO-SGB. It was in the days of position reports and I think it was 11 minutes from BPK to overhead EGNX at 'jet speed'.
Bedford became BEDFO, but I think Hucknall was withdrawn. The charts are in my loft somewhere.
By the time I joined NATS in 1979, Upper Amber 39 had become Upper Blue 4, later to become Upper Bravo 4 and then Upper November 601. N601 was bolted on below.