A puzzle. The operating crew usually start with the 1450 flight IOM to LCY so they have enough hours available to allow for most delays. BA.com report Sunday's BA3288 departed LCY at 2035, and this mornings early flight left on time seemingly confirming the aircraft had reached IOM the night before. So SOE not sure where your info comes from?
Having said that I know from experience that if I see the Saab taxying towards the stands at the far west of the apron the departure will be delayed. But as the return flight doesn't involve a sightseeing trip down the east coast before a long run up the Thames Estuary the crew can usually make some of that time up.