Crossrail have announced another delay to the Elizabeth line.
The central section between Paddington and Abbey Wood is now not due to open until the start of 2022.
The Board said there may be opportunity to review and bring forward the opening depending on progress during the "intensive operational testing phase."
As well as delays the board also announced that the completion cost for the Crossrail project could be up to £1.1bn above the financing package agreed in December 2018 - requiring an extra £450m in funding.
Crossrail said operational testing, known as trial running will begin at the earliest opportunity in 2021.
After trial running it will then need to fully test the Elizabeth Line before it can open up safely to passengers.
This includes a final phase known as Trial operations involving people being invited onto trains and stations to test real-time service scenarios to ensure the railway is ready to fully open.
Once the central section is opened, full services across the Elizabeth line from Reading and Heathrow in the west to Abbey Wood and Shenfield in the east will be introduced.
The full service will be aligned with the National Rail timetable change which occurs twice a year in May and December.
Crossrail said the impact of covid-19 has made the existing pressures more acute.
They said the latest delay is due to three main factors.
Routeway : we have had lower than planned productivity in the final completion and handover of the shafts and portals. The shafts and portals form a critical part of the routeway and contain many of the complex operating systems for the Elizabeth line. We have now completed handover of eight of the ten shafts and portals to TfL and will complete handover of the final two this autumn.
Stations: we have revised our previous schedule assumptions about the pace at which these large and complex stations can be handed over to TfL. The completion and handover of all the stations in the central section is a monumental task - in our updated plan we have phased the transfer of stations to take account the scale of this undertaking.
COVID-19: Covid has further exacerbated the schedule pressures due to a pause of physical activity on sites during lockdown to keep the workforce safe and significant constraints on ongoing work and productivity due to the reduced numbers that can work on site to meet strict social distancing requirements. We now have a maximum of around 2,000 people on our sites, less than 50 per cent of our pre-Covid complement.
Crossrail's Chief Executive, Mark Wild said despite the delays their focus is on opening the Elizabeth Line as soon as possible.
But the Mayor of London, Sadiq Khan said he's "deeply disappointed" by Crossrail's updated schedule.
He's asked for TfL's new commissioner, Andy Byford, to review Crossrail's latest plans - including their estimated additional costs.
He urges Crossrail to work with the Department for Transport to ensure "everything possible is being done to get the central section safely open as quickly as possible."