FR 6974 then BA 477 at Barcelona
Rome → Barcelona → London Heathrow
Timetable, Barcelona time
14:55FR 6974 from Rome at the gate
12:30BA 477 to London Heathrow leaves the gate
21 h 35 apart on the timetable, overnight
BA 477 leaves 21 h 35 after FR 6974 arrives on the timetable: more than half a day, so not a connection we count.