Causes The block telegraph instruments at Charfield had three different positions: train on line, line clear and line blocked. Not only was it in control of the station and sidings, the signal box was a block post for two sections: Berkeley Road to Charfield (up line) and Charfield to Wickwar (down line), and was in control of signals for the entrance to the station and the following block sections on each line. (This was standard block working – even though the box may control a section it controlled the signals for the entrance to next section along the line.) The down line signals protected trains in both the down line of the station and Charfield to Wickwar section of the down line which followed. It was on the down line that events would occur. The block instrument could not be set to line clear until the train on the line had passed over a treadle at the next signal box and the signalman in the box had sent his consent by telegraph. The Block instruments were interlocked with the signal levers so that unless the respective instrument stood at 'line clear', they could not be cleared to accept a train. This prevented any false signals being given by mistake. When the GWR goods passed Button's 'clearing point' signal (the end of the section) at 5:13 am, it released the treadle and thus allowed the section from Berkeley road to Charfield to be cleared. He then shouted to Gilbert and Sutton of the goods train to shunt and 'pulled off' his shunting disc signal. At this time, nothing was out of the ordinary. It was less than an hour before dawn, and the railway tracks were shrouded with fog. Due to the fog, Button could not see his down distant signal or his down outer home signal (both were connected to electrical repeaters which showed the signal position via an instrument in his box), but he could see his 'fog object' and therefore saw no need to call out fogmen. The section from Berkeley Road to Charfield was clear, and therefore Button could accept the LMS night mail from Smith. He was perfectly justified in doing so, given that had a quarter of a mile clear between the clearing point signal and his outer home signal (the first "stop" signal controlled by Charfield box)- there was plenty of space for the