The modernisation of four tube lines is to be delayed by up to five years following the embarrassing failure of a £350m project to install new signals.
The high-tech upgrade of the Circle, District, Hammersmith & City and Metropolitan lines was due to finish in 2018.
But Transport for London today confirmed a revised target date of 2023 for the new system.
TfL claims the improvements will mean 'faster and more frequent' services with trains every two minutes in central London.
The original £354m contract with Bombardier was scrapped in 2013 after tube bosses concluded the system might not work.
The project has now been handed to a new supplier, Thales, with a revised price tag of £760m.
TfL admits it is unable to meet the original 2018 target for work on all four 'sub-surface' lines to be finished.