Archi - the flaps were always down (needed!) for take-off, the problem was that No 1 burner (top) lit fully, but No2 nozzle opened fully but did not light and stayed fully open which equalled around 40% less cold thrust on No2, resulting nose-down pitch prevented rotation and the resulting attempt on the world land-speed record removed the barrier and frightened British Rail, as I recall. Two great characters invloved, one I know is sadly now deceased, the other who was my conversion QFI I have no trace of. I airtested the aircraft SEVERAL months later.