As Evalu8er said, the oil charter did operate a 747SP for a while. It did do the Northbound sector direct Mt Pleasant-Stansted, (think it was about a 14 hour flight) but I seem to remember the southbound flight was via Recife, Brasil, due to the distance to alternates from the Falklands. The required payloads on the flight were quite light, as they were only taking 100 or fewer pax on each crew change flight.