The proposed multi-billion pound High Speed 2 (HS2) rail line connecting London to Manchester and Birmingham to Leeds should go ahead, despite it running over budget, according to a review.
Douglas Oakervee, the former Chair of HS2, was given the task of assessing the viability of the project by Prime Minister Boris Johnson.
His review has been leaked and has ruled out axing parts of the project to save money.
The report, leaked to the Times, also found that HS2 could benefit cities in the North and Midlands more than London, because of the improved conditions on intercity lines.
Mr Oakervee said journey times from Leeds to Birmingham would be more than halved - from two hours to just 45 minutes.
The review argues that if HS2 were cancelled it could take another decade for alternative rail schemes to be developed in its place.
The main HS2 London terminus at Euston should be retained, with more stations added later, it concludes.
A 10-person panel advising the review had suggested axing the eastern arm of the line's second phase (running from Birmingham to Leeds) and ending HS2 at Old Oak Common in West London, instead of at London Euston.
Panel members have been shown a copy of the draft review, as the pre-election Purdah period comes into effect, preventing politically sensitive releases from the Civil Service.
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The report concedes HS2 is "not affordable" within the £56 billion budget that had been set for the project in 2015, but a revised £88 billion budget is expected to increase again.
Mr Oakervee has submitted plans to cut the number of trains per hour from 18 to 14, according to the document.
The timing of the leak adds to pressure on Prime Minister Boris Johnson to clarify whether a Conservative Government would derail the project or press ahead with it.
He had sought a delay on a final decision until after next month's General Election.
Last week, Mr Johnson indicated he was wary of putting HS2 on the "scrap heap," but he conceded it was "incredibly expensive".
He told Birmingham Live on a previous occasion that the cost would "probably be north of £100 billion."
Opponents of HS2 claim the review had been a "whitewash" as Business Secretary Andrea Leadsom described it in October as "insensitive" and "out of control."
In September, the Transport Minister Grant Shapps said the first phase of the railway would be delayed by up to five years.
It had been due to open at the end of 2026, but it could now be between 2028 and 2031 before the first trains run on the route.
The second phase - from Birmingham to Manchester and Leeds - had been anticipated to open in 2032 or 2033, but this has been pushed back to between 2035 and 2040.
In August, the Government said it planned to review the costs and benefits of HS2 with a decision whether to go ahead or not expected by the end of 2019.
Trains on HS2 would be 400 metres long with more than 1,000 seats and capable of speeds of 250 miles per hour.
Once the second phase is complete, Manchester to London journey times would take one hour and seven minutes (down by 60 minutes).
