Failed Tube maintenance company Metronet has been taken over by Transport for London (TfL).
Metronet, which was responsible for maintaining eight of the 11 London Underground lines, went into administration in July last year after running into financial difficulties.
The firm's collapse sparked fierce criticism of the public private partnership arrangements to upgrade the capital's underground network.
TfL pledged to make the Tube more reliable and increase passenger capacity by investing in new trains, signalling systems and station revamps.
Spending on the eight lines that were previously Metronet's responsibility is forecast to be about £1.4 billion over the coming financial year, it said.
London Mayor Boris Johnson said: "Since Metronet went into administration there has been a protracted period of uncertainty, resulting in the millions who rely on the Tube not knowing when the needed improvements would be delivered.
"With Metronet now out of administration and under the control of TfL we can ensure that the crucial upgrade work is continued and delivered on time, while representing good value for the capital.
"Londoners deserve nothing less, and I will be working closely with TfL to make sure that the improvements are delivered."
London Underground managing director Tim O'Toole added: "We're working hard to deliver our renewal programme efficiently.
"We have already overseen the restructure of a number of contracts, particularly the train and signalling contracts for the sub-surface lines, and track maintenance across all these eight Tube lines."
