Mayor Boris Johnson has revealed “significant progress” towards completing signalling upgrades on the Jubilee line, part of much-needed investment to provide extra capacity on the network.

Transport for London stepped in to buy contractor Tube Lines for £310m in June last year after Jubilee and Northern line upgrades fell behind schedule as wrangles broke out over line access.

Johnson, said: “Work has been progressing swiftly since TfL took control of Tube Lines and we can now see real milestones being reached, including the long awaited completion of this crucial upgrade in just a few months time.

“This is good news for the many thousands of passengers who rely on the line, and clearly demonstrates how our hands on approach to the upgrades is making real improvements.”

TfL retained the staff at Tube Lines – including leading industry experts – needed to take forward the remaining projects.

Mike Brown, managing director for LU, said: “This major milestone represents one of the first fruits of TfL taking direct control of the Tube upgrades after the failure of the PPP system to deliver.

“We inherited a Jubilee line upgrade that had been frustrating and painful for passengers and businesses, and we have been working around the clock to complete the work as quickly as possible.

“A successful conclusion is now in sight – with the upgrade on track for completion in the spring of this year.”

By the end of the current programme in 2020 there will be 30% more capacity on the Underground.