They were obtained to get Britannia in the affinity group charters which later became advance booking charters. These allowed members of a club to travel together on charter flights, but the rules surrounding them were widely flaunted. In 1973 the rules required operators of these flights to set up a U.S office and Britannia decided it was not worth their while and disposed of the aircraft. They did do other things - freight charters, racehorses as well as IT flights to the Canaries etc. I remember one going to Kuala Lumper once.