Not any more. BA now flies LHR-BKK, and QF SYD-BKK.
On the LHR-SIN-SYD route there are some flights like this.

All comes down to what approvals they have - eg the AA/BA JVs , or the QF/BA JSAs - otherwise agreed scheduling may be deemed anti-competitive.

Finally might be the only times that work due to scheduling, curfews, use of aircraft overnight before domestic peaks.