I flew from Stansted to Aden on or about 6/7 October 1963 in a BUA Britannia and it was with rear facing seats, about 11 hours.
We came back around 6/7 October 1964 and were lucky enough to be on one of the recently introduced VC10 trooping flights, about seven hours. Shortly after that it was back to the Britannia as the VC10s were needed for the newly acquired South American routes.