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.