The report noted that while the fog had lifted in the vicinity of Harrow station, with visibility improving to witnesses estimated visibility at the Up Fast Distant to be . At , this would be covered in four seconds or less. In these circumstances I can only suggest that .."the driver".. must have relaxed his concentration on the signals for some unexplained reason, which may have been quite trivial, at any rate during the few seconds for which the Distant signal could have been seen from the engine at the speed he was running in a deceptive patch of denser fog. Having thus missed the Distant he may have continued forward past station (which was not on his own side), underestimating the distance he had run from and still expecting to see the colour light and not the Harrow semaphore stop signals which were at a considerably higher elevation.