Four major tasks remain: to build and test software to integrate the train operating system with three different signalling systems; to install and test station systems; to complete the installation of equipment in tunnels and test communication systems; and to run trial trains.

Crossrail expects that the remaining fit out and systems installation in the stations and tunnels will complete this year. Development of train and signalling software to allow the train control system to be fully tested is also expected to complete by the end of 2019.

Design and delivery challenges are said to remain at Bond Street, with Crossrail promising to work alongside a Costain Skanska joint venture to ensure the station is ready at the earliest opportunity.

Crossrail adds that dynamic testing of the trains in the tunnels is now under way. Trains have been operating at line speed in the central section using the new automatic signalling system and multi train testing will soon get under way.

The project’s chief executive Mark Wild said the new plan allows Crossrail and its contractors “to put the project back on track”.

London Assembly Transport Committee chair Caroline Pidgeon said of the new launch date window: “We welcome this announcement with cautionary relief. However, the project has been pushed back twice already, so the question has to be asked – is the ‘six month window’ a hedge betting exercise to avoid disappointing passengers once more?”

“Londoners are forking out £30 million a week to bring Crossrail to completion. Further delays and doubtful dates are simply not an option.”

London Mayor Sadiq Khan said: “I was deeply angry and frustrated when we found out about the delay to Crossrail last year. We now have a new leadership team who have worked hard over recent months to establish a realistic and deliverable schedule for the opening of the project.”

Trade Union TSSA general secretary Manual Cortes called for a public inquiry into the delay and said that Londoners will not be fooled by the fact there is “nothing concrete about when full services will commence”.

(Photograph: Crossrail/TfL)