Tube passengers endured further travel misery today, with severe delays on three Underground lines.
The hold-ups, which included part-suspension of services on two lines, followed a series of problems on the Tube last week.
Today's difficulties were due to signal failures at West Ham in east London and at Temple in central London.
The failures led to a part-suspension of the Hammersmith & City and District lines between Liverpool Street and Barking and severe delays on the rest of the two lines as well as severe delays on the Circle line.
The Circle and District lines were among the routes affected by problems on the Underground last week during the first hot spell of weather of the year.
Several hundred passengers had to be led through a tunnel on Wednesday evening after a Jubilee Line train broke down, and are to be paid £40 each in compensation.
Last Tuesday morning, as many as six Tube lines were hit by delays during one period of the rush-hour.
The delays prompted the RMT union, which has complained of cut-backs in staff, to call for an inquiry into the running of the Underground.
These calls were repeated today. The union's leader Bob Crow said: “The chaos of last week has spilled over into this week despite the barrage of lies and excuses from London Mayor Boris Johnson and his officials.
“This cuts-led crisis cannot be allowed to drag on into the Olympic Games when three million extra journeys will be thrown at a system that clearly cannot cope with routine demand.
“The reality of years of cutbacks to maintenance schedules, track patrols and staffing levels has hit home with a vengeance in the past week and the fact that Boris Johnson and his officials are living on a prayer day in and day out is now exposed for all to see.”
Labour's London Assembly transport spokeswoman Val Shawcross said: "The scale of the daily Tube delays we are seeing is completely unacceptable.
"Millions of Londoners who use the Tube every day deserve better than the terrible services they are being forced to endure. Boris Johnson needs to take responsibility and urgently get a grip of the problem."
London Underground operations director Nigel Holness said Tube technicians were working as quickly as possible to repair the faults.
He said: "Trains are moving through the area but more slowly than usual, so customers are advised to use other services where possible. I apologise to customers who have experienced delays this morning."