London's mayor has been pressed to take urgent action to tackle Tube delays as passengers suffered fresh problems.
Labour's mayoral candidate Ken Livingstone told Boris Johnson he had to "get a grip" on the Tube "chaos".
Over the past month there has been "serious disruption" on one or more Underground line every single day, the Labour former London mayor claimed.
But the mayor's transport adviser Kulveer Ranger rejected the comments as "easy rhetoric".
Commuters faced delays in Monday morning's rush hour because of signal failures on the District and Piccadilly lines and a lack of available trains on the Metropolitan Line.
'Eye off the ball'
"Londoners are fed up with the daily delays on the Tube," said Mr Livingstone.
Labour London Assembly transport spokeswoman Val Shawcross said: "The mayor has taken his eye off the ball on his key responsibility of keeping the Tube running."
Mr Ranger said: "The mayor watches the levels of service on the Tube from a screen in his office like a hawk and is in constant contact with Tube chiefs about what needs to be done.
"We utterly reject the easy rhetoric and gall of the former mayor who refused to condemn recent strikes and left behind a gaping black hole in finances, as well as Tube upgrades that were spiralling over budget and over time."
In the past month Londoners have faced delays on the Tube because of over-running repairs, cracks on the lines, signal failures and faulty trains.
They have been forced to abandon trains and walk through tunnels on a number of occasions following failures on the Underground network.
And a 24-hour strike was held on the network from the evening of 1 November - the third walk-out this year in a row over threatened job losses.
A fourth strike is planned for 28 November but union leaders have said they have no plans to disrupt services over Christmas and the new year.