Back in the late 60's, when I acquired my first airband radio, most UK airlines were still using the aircraft registration for their ATC callsign. Exceptions I remember were BOAC (Speedbird), Caledonian, Laker, British Eagle, Monarch, who used flight numbers from day one (April 1968), possibly Cambrian also. BEA switched to flight numbers around April 1969 IIRC - I remember a Heathrow visit on 13/4/69 and being somewhat dismayed when I found out. Most European operators, on the other hand, used flight numbers. Sabena were one exception who were still using registrations until at least 1977. Surprisingly, most of the US supplemental carriers seemed to be using registrations - I remember hearing Overseas National DC-8's, World 707's, Capitol DC-8's and American Flyers 727's all calling with registrations on 124.6 Mhz around 1969, which was the frequency controlling what then was Amber 1 Lichfield-Daventry-Woodley and Amber 2 Detling-Brookmans Park-Daventry.
What I am looking for is any info on when UK airlines switched to flight numbers. I think most were around the mid 70's when computerised flight plans came into use. Exceptions were still about, mainly positioning sectors and training flights. Also which foreign operators still used registrations - can anyone confirm Air France used registrations and when they switched to flight numbers. I seem to remember the Tarom IL-18's operating IT flights to the UK in the early 70's were using registrations - did they also use them for their scheduled flights to the UK? Info on Adria, Condorflug and Bavaria would also be helpful.