Not sure if this is the sitution here, but BA would, (possibly still do), push on schedule from SIN to LHR but then slow right down en route in order not to arrive too early at LHR. This is very aggravating for following traffic as the ATC clearance for BA would invariably contain a mach number of "not less than" but once out of SIN airspace this was abandoned totally and everyone following then suffered from the imposition of unrealistic speeds and/or flight levels. Conversations on freq 123.45 generally, (but not always), revealed a "stuff you Jack, I'm alright" kind of response. Possibly, in this instance, ATC were able to chase them up along the way and ensure they kept a reasonable speed at the risk of being descended to a seriously unrealistic FL?
From a friend in BA on the B747-400 I understand that on time departures and arrivals within twenty minutes of schedule are paramount?