The opening of a section of Crossrail could face more delays, it has emerged.
More time is needed to test trains before the huge project is serving the whole of the capital.
It has emerged this morning that it will not be open until Autumn 2021 at the earliest.
The massive infrastructure project has already been cursed with endless delays and budget blowouts. It is now estimated to cost more than £18billion.
The new line - to be called Elizabeth Line - was initially supposed to open in December 2018 but now the testing period for trains won't commence until July this year.
"From the start of trial running, the conventional wisdom is nine to 12 months to shake it down," Mark Wild, Crossrail chief, said.
"The reason we might be able to mitigate that and reduce that period is if we get good quality software in February or March - we could start shaking the system down earlier than the defined start of the trial running."
Eventually, the Elizabeth Line will link up Reading in Berkshire and Heathrow Airport to Shenfield, Essex, and Abbey Wood, southeast London.
The section thought to be affected by the latest delay is between Paddington and Abbey Wood.
But Sadiq Khan insists the whole service will be open as soon as possible.
A spokesman for the mayor of London said: "The Elizabeth Line will open as soon as practically possible in 2021."
Mirror Online has contacted Transport for London.
