The first part of Crossrail will be opened by March 2021 at the latest, those behind the delayed project have pledged.

A "robust and realistic plan" is said to have been formed by the new Crossrail leadership team and agreed by the Crossrail Ltd Board to put the project back on track.

Crossrail, which will be known as the Elizabeth line when it opens, was due to launch in London in December but has been delayed after a series of problems.

The new plan involves a "delivery window" between October next year and March 2021, but even then Bond Street station will not be ready, the company has confirmed.

Crossrail Ltd said the central section, between Paddington and Abbey Wood, is expected to open during 2020, although it could be as late as March 2021, with initially 12 trains per hour at peak times.

But Bond Street is delayed because of "design and delivery challenges" and will not open at the same time, with Crossrail expecting it to be ready some time in 2021.

After the central section has opened, Crossrail said full services across the line from Reading and Heathrow in the west to Abbey Wood and Shenfield in the east will begin "as soon as possible".

The company said that as work continues there will be regular "progress reports" for Londoners and "increasingly specific estimates" of when the line will open.

Mark Wild, chief executive at Crossrail Ltd, said: "I share the frustration of Londoners that the huge benefits of the Elizabeth line are not yet with us.

"But this plan allows Crossrail Ltd and its contractors to put the project back on track to deliver the Elizabeth line. Crossrail is an immensely complex project and there will be challenges ahead particularly with the testing of the train and signalling systems but the Elizabeth line is going to be incredible for London and really will be worth the wait.

"This new plan will get us there and allow this fantastic new railway to open around the end of next year."

Tony Meggs, chairman at Crossrail Ltd, said: "The Crossrail Board will be holding the leadership team to account as they work to complete the railway.

"We will be open and transparent about our progress and will be providing Londoners and London businesses with regular updates as we seek to rebuild trust with all our stakeholders."

Mayor of London Sadiq Khan said the new leadership team had worked hard to come up with a "realistic and deliverable schedule for the opening of the project, which TfL and the Department for Transport will now review".

He added: "Crossrail is a hugely complex project. With strengthened governance and scrutiny in place, TfL and the Department for Transport, as joint sponsors, will continue to hold the new leadership to account to ensure it is doing everything it can to open Crossrail safely and as soon as possible.

The chairwoman of the London Assembly Transport Committee, Caroline Pidgeon, said she welcomed the projected opening date with "cautionary relief", adding: "The question has to be asked - is the 'six-month window' a hedge-betting exercise to avoid disappointing passengers once more?"

The announcement of the new timetable for progress came as Transport for London's (TfL) commissioner refused to resign over the delayed project.

Mike Brown declared that he is "fit to be in position" and has the "full support" of Mr Khan.

A report published by the London Assembly Transport Committee on Tuesday stated that Mr Brown, who has held the role at TfL since September 2015, "altered key messages of risk" on deadlines on the project which were sent to Mr Khan's office.

The report recommended that Mr Brown, appointed by Boris Johnson when he was mayor and paid at least £350,000 in 2017/18, "reflect(s) on whether he is fit to continue to fulfil his role".

Giving evidence to the committee on Thursday, Mr Brown said: "I'm not reflecting on whether I'm fit to be in position. I believe I am.

"I've got the full support of the mayor and that's the end of that issue from my point of view."

Mr Khan's office has said he has "every confidence" in Mr Brown, adding that the previous leadership of Crossrail were responsible for providing "inadequate information" about the delays.

Crossrail's delay has resulted in a row over when Mr Khan knew the railway would not open on time.

He claims he only found out on August 29, two days before Londoners were informed, but Crossrail Ltd's former chairman Sir Terry Morgan insists the mayor was aware of problems at least a month beforehand.

Sir Terry resigned as chairman of HS2 Ltd and Crossrail Ltd - a TfL subsidiary - in December.

The project's budget has fluctuated from £15.9 billion in 2007 to £14.8 billion in 2010.

But due to the cost of the delayed opening, a £2 billion Government bailout of loans and cash was announced in December.

David Frost, chief executive of London Chamber of Commerce, said: "I am glad to see a firm commitment to a date for the opening of the central section of Crossrail.

"Many businesses have already made investment decisions based upon the route and will want to see these starting to pay off.

"I am concerned though that no timetable is set to open the full line, including the link to Heathrow.

"It is of huge importance to London that this happens as soon as possible."