If the nose was lifted and then the brakes applied at LHR, a 747 will trundle off the end at quite a hefty speed. Nothing has been said about it within the company so I would assume a stall/surge of some sort. (happens quite regularly so non event really). The fact that you said no reverse was selected means the aircraft was not above 100knots. I know as a pax it can seem quite a hair raising experience, however it is a well practiced event. I'm surprised no information was passed to you from the flight crew after the event.
For those attacking BA pilots (again), please don't tar us all with the same brush like the Independant (today's front page). Most of us are 100% professional and take a huge amount of pride in our jobs.
Regards.
