 The accident was caused by a signal technician carrying out a temporary repair to a faulty signal even though he was not familiar with the layout and did not have access to the signalling diagram.During the morning rush hour, the advanced platform starter signal on the northbound line at Waterloo station had developed an intermittent right side fault which sometimes caused it to show 'danger' even though the line ahead was clear.This was causing significant delay to the service because drivers were having to carry out the 'stop and proceed' rule which required them to wait one minute, pass the signal and then proceed slowly with caution as far as the next signal.