Flight Changi Airport departs from Singapore Changi Airport at 23:20 and arrives at London Heathrow Airport at 06:30.
The flighttime is about 14h 10m. The distance travelled ("as the bird flies"): 11049 Km. So the average speed is roughly 780 Km.
There is an 7 hour time difference between Singapore and London
The best day to arrive at Singapore is Saturday and it would be best to avoid Thursday, as prices are on average 119% higher than on Saturday. (Average prices, based on 162814 datapoints.)
We have a lot more statistics for flights BA 12 and between Singapore and London.