We were #1 at the holding point when Concorde departed on 21/1/76 (the 747 in BOAC colours if you ever see the video). The long delay waiting to co-ordinate with Air France caused us to divert from New York to Boston as the vis went below limits at about 2000ft on the approach into KJFK.
Airclues
PS....at least I got the Concorde crew to sign my first day cover while standing next to them during flight planning.