A senior source has told the BBC that Crossrail could be delayed again until 2021.

The warning comes just weeks after MPs on the Public Accounts Committee demanded the Department for Transport (DfT) explain who is responsible for ‘failures’ on the project, which was due to be completed in December 2018.

Crossrail has said testing of trains and signalling on what will be the Elizabeth Line when it opens is “progressing well”.

But according to the BBC, a senior source involved in the multi-billion-pound project said the ‘dynamic testing’ phase was “proving more difficult than was first thought”. They warned that “the last quarter of this year will be a critical period for the testing”.

While the source agreed that in the current state of the project, the “best case scenario” would be the line opening to the public in spring 2020, while a “middle probability case” would see it launch next summer.

However, a “worst case” scenario would mean the Elizabeth Line not fully opening until the spring of 2021.

According to rail sources, the uncertainty surrounding Crossrail comes from the fact that matching a new signalling system in the tunnels with software on the trains is still ongoing.

Many of the stations along the route are not complete – most notably Paddington and Bond Street, which are the furthest behind schedule.

The 2021 estimate is in line with the Public Accounts Committee’s report, which said MPs are “not convinced that new services will start to run in 2020 as now hoped”.

The Crossrail project is running nearly £3 billion over budget already after receiving a cash injection from the government and Transport for London (TfL), though auditor KPMG released a report claiming the development is costing £30 million a week.

Subscribe to the BBT Newsletter

Join the Buying Business Travelk newsletter for the latest business travel buying news.

Thank you for signing up!