1HourPhoto,

As Sigwx says, it's down the the planned track over the North Atlantic.

Also, due to the fact that the majority of departures from LHR are south- and westbound, as oppoesed to northbound, airlines sometimes re-file the North Atlantic route from a westbound (the Compton route - which heads out over Reading, then out over South Wales, or the Southampton route - which turns west over Southampton and then routes along the South Coast to Cornwall) to a northbound (WOBUN departure - turns north at Maidenhead towards Birmingham) to avoid any start delays on south- and westbound departures. This may have been a case where BA filed a northbound route to avoid any possible delays at start up; they would decide that the extra fuel burnt/time taken to fly northabout would be comensated by the on time departure.