Direct flight from London to Tokyo, with flying over Norway and Russia, 13 hours and 50 min. Direct flight from Tokyo to Sydney, 9 hours and 40 min. Brings the total flight time to 23 hours and 30 min, between London and Sydney.

Edit: According to British Airways, non stop flight time from London to Tokyo is 11 hours and 40 min.

https://www.prokerala.com/travel/flight-time/from-london/to-tokyo/

Direct flight from London to Tokyo, with flying over Norway and Russia, 13 hours and 50 min. Direct flight from Tokyo to Sydney, 9 hours and 40 min. Brings the total flight time to 23 hours and 30 min, between London and Sydney.