Central Line closed by two separate Tube faults
A total communication failure between trains and controllers led to a two-hour shutdown of an entire London Underground 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.
A normal service on the Central Line had resumed by 1800 GMT on Tuesday.
Bob Crow, of the Rail, Maritime and Transport (RMT) union, said it had been "another round of chaos on the Tube".
The first breakdown - involving a signal at White City - led to the Central Line being suspended from Marble Arch to North Acton from 1115 to 1200 GMT.
Two trains were stuck outside White City station as a result.
After 40 minutes one was moved to Shepherd's Bush station, where passengers were allowed to leave, and after 50 minutes the other was taken to East Acton.
'Screaming down phone'
Fifteen minutes later, the entire Central Line was closed and all drivers were ordered to stop their trains in the nearest station under a "code amber" alert, the sources added.
The communications breakdown took until 1415 GMT to clear.
The problems happened the day after what Mr Crow called "a rush-hour from hell".
The Waterloo and City Line was suspended on Monday morning, with a signal failure disrupting the Victoria Line and other problems on the Jubilee Line.
And disruption to the Jubilee Line on Friday led to Mayor Boris Johnson "screaming down the phone" at London's transport commissioner Peter Hendy, sources at City Hall said.
Mike Brown, London Underground's managing director, said: "Of course I apologise for every single disruptive journey a passenger ever has.
"But in the context of 4m people using the Tube network every day, our reliability is steadily improving.
"You can't update a railway which dates back to the Victoria era overnight."
But Mr Crow said: "Still the mayor and TfL tell us that it's OK to cut staff, track patrols and signalling maintenance frequencies to the bone.
"Privatisation, cutbacks and skimping are taking a heavy toll on what should be one of the world's showcase metro systems, and with the Olympics just around the corner, we need an end to these cuts and a change of direction."