Central Line problems: Tube boss 'sorry' over delays
London Underground's managing director has apologised after a day of disruption on the Central Line.
A total communication failure between trains and controllers led to a two-hour shutdown of the line, sources have said.
It happened minutes after a separate signalling problem on the same line left passengers stranded in one train for 50 minutes and another for 40.
Bob Crow, of the Rail, Maritime and Transport (RMT) union, said it had been "another round of chaos on the Tube".
But Mike Brown, London Underground's managing director, said: "In the context of four million people using the Tube network every day, our reliability is steadily improving."