The Elizabeth line was due to start taking passengers this December.
But the opening through central London has now been pushed back to “autumn 2019”.
The Enquirer has reported repeatedly about Crosssrail’s problems during the crucial fit out phase.
Project chiefs repeated the mantra constantly that the job was “on time and on budget”.
It is now £590m over budget and nine months late.
Crossrail said: “Crossrail Limited has been working hard to maintain the programme and sufficient testing time is required to introduce the next phase of the railway – the central section between Paddington and Abbey Wood – in a way that can be guaranteed to be safe and reliable.
“The original programme for testing has been compressed by more time being needed by contractors to complete fit-out activity in the central tunnels and the development of railway systems software.
“Testing has started but further time is required to complete the full range of integrated tests.”
One subcontractor said: “Pardon my French but what a f*****g shock.”
Simon Wright, Crossrail Chief Executive said: “We have made huge progress with the delivery of this incredible project but we need further time to complete the testing of the new railway.
“We are working around the clock with our supply chain and Transport for London to complete and commission the Elizabeth line.”