thanks for your help BD and kiwiflyer,

After checking of timetables i've found Qantas.com shows 2 departures from LHR-SIN daily, 12.15 & 22.05. BA.com matches this for times but not for flight numbers so can only assume they are one and the same.

The Qantas.com timetables show it as everyday a 747 but i suppose they refer to current flights.

I did some dummy bookings for my dates on Qantas.com in april and found the A380 flights are leaving LHR at 12.15 every other day so regardless of what BA calls the flight i believe i've found the big boy.

Jim