Transport for London (TfL) today apologised to thousands of commuters and other travellers hit by fresh delays to Tube services, ahead of a weekend of closures because of engineering work.
There was disruption on the Jubilee, Victoria, District and Central lines because of unrelated power, rolling stock and signalling problems.
"We are sorry for the inconvenience experienced by a number of our passengers this morning," said a spokesman.
"The impact that incidents have on passenger journeys on average has reduced by over 20% since 2003 and failure of infrastructure such as signals, track and trains as the cause of incidents have declined by over 40% since 2003/04.
"We are working around the clock to improve reliability and to rebuild every part of the Tube, the world's oldest underground network.
"Our work - increasing capacity by 30% through new trains, signalling and track, and rebuilding key stations - will mean better, quicker, more comfortable journeys for passengers," the spokesman added.
The Circle, District, Hammersmith & City, Jubilee and Metropolitan lines, and the Docklands Light Railway and London Overground will all be affected by engineering work this weekend, while the Victoria Line will be closed completely on Saturday and Sunday due to line upgrade work, hitting thousands of football fans going to the Tottenham v West Ham game tomorrow.
Meanwhile TfL announced a crackdown on fare dodgers after new figures showed that fare evasion was costing almost £75 million a year.
Plain clothes ticket inspectors will carry out increasing numbers of checks across the capital's transport network.
London's Mayor Boris Johnson said: "Fare dodgers are a parasitic scourge on this city, costing London millions of pounds."