 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.The signal lineman for the area was unavailable and so one was summoned from Kennington station.