BA 138 then BA 870 at Heathrow
Mumbai → London → Budapest
Timetable, London time
07:05BA 138 from Mumbai at the gate
19:45BA 870 to Budapest leaves the gate
12 h 40 apart on the timetable
BA 870 leaves 12 h 40 after BA 138 arrives on the timetable: more than half a day, so not a connection we count.