Trains were worked by time interval system, with signalmen controlling entrance to tunnel and both ends linked by telegraph. There were three trains in succession. First entered tunnel. Second approached and was signalled to stop. Driver ran past into tunnel. Signalman telegraphed to find out if first train had then left other end of tunnel. Signalman at the other end thought he was referring to the first train and replied train clear. Meanwhile second train had stopped and driver was reversing. Third train was allowed into tunnel.