The opening of London's Crossrail has been pushed back by nine months.
Project leaders have said more time is needed to complete the final infrastructure and extensive testing between Abbey Wood and Paddington on the line that will be re-named the Elizabeth line upon opening.
The £15billion scheme is already almost over £600 million over budget.
The ten-year project, Europe's largest construction project, delivered by Crossrail, brings together multiple infrastructure contracts, new trains and three different signalling system, and will increase central London’s rail capacity by 10%, with an estimated boost to the economy of £42 billion.
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 (TfL) to complete and commission the Elizabeth line.”
The new railway, jointly sponsored by the Department for Transport and TfL with support from London's business community, will connect stations such as Paddington to Canary Wharf in 17 minutes and bring an extra 1.5 million people to within 45 minutes of central London; more than 200 million passengers are expected to use it a year.
Crossrail trains are already operating between Shenfield and Liverpool Street (mainline) between Paddington (mainline) and Hayes & Harlington.
"We've already surpassed one degree of global warming," said Kristen Buida, manager of the London Climate Change Partnership.