Cube master
As has been pointed out the delay could have been down to a whole host of reasons such as ATC slot, resolving a technical problem, resolving a loading/baggage problem....the list is almost endless.
You could keep an eye on websites such as "The ba source" (I'll let Google be your friend) but since the flight did eventually depart and subsequently arrived at destination I doubt they'll mention it.
Chances are in the scheme of things the reason was trivial and certainly anyone who knows for certain by virtue of access to privileged info (e.g company sources) or by virtue of listening to the radio
is probably not going to admit to the fact, though you might get lucky if somebody drops in who was actually on the flight..