Parliamentary wrangles over High Speed Rail (HS2) are pushing up the price of the project, the network's chairman has said, in a report which will be seen as a direct challenge to Ed Balls.
David Higgins' report on the infrastructure project suggested that the time table should be substantially cut, with a finish date of 2027 rather than 2033, in a bid to cut costs.
Such a move could potentially save billions of pounds, but would rely on the myriad HS2 bills passing through parliament being passed more quickly.
The comment is a tacit challenge to Balls, who has raised the prospect of Labour ending its support for the project unless costs are kept down.
Last week, Balls said Higgins needed to show costs "have come down markedly", but the report does not include any precise financial figures.
However, Higgins' report ruled out any major cost-savings as "irresponsible" because they would cut measures aimed at protecting local residents from noise and inconvenience.
Instead, he put the onus on Labour by suggesting it is parliament itself which can keep the price down by hurrying up its end of the deal.
"There is a direct connection between the length of time the parliamentary process takes, and the amount of contingency that is required," he will say.
The current whole-line cost, including contingencies, is £42.6 billion, excluding £7.5 billion for the trains.
"Bringing forward work will not be as simple as it sounds. Unless there are plans to circumnavigate the statute book, then a separate hybrid bill will have to be introduced," Richard Houghton of HS2 Action Alliance said.
Higgins' report says the second, northern phase of the line, which works in a Y-shape from the north-west to the north-east, should be worked on at the same time as the initial London-to-Birmingham section.
He also recommended that the line stretch an extra 43 miles north to link up with a new transport hub in Crewe in Cheshire.
This would help unlock a bottleneck on the current network and fast-track benefits for Liverpool and North Wales by up to six years.
The proposal is being put out to consultation.
The report suggests that plans to link HS1 to HS2 should be scrapped, meaning there would be no London to Kent Channel Tunnel high-speed rail link and therefore no direct-connection between English cities and the continent.
That suggestion was quickly accepted by transport secretary Patrick McLoughlin, who said it had been removed from the bill.
The scrapping of the link-up may ease opposition to HS2 in the capital, because it would end plans to disrupt freight and underground services and run the line through Camden market.
As a further London sweetener, Higgins also suggested using the opportunity for a major redevelopment of Euston station, so the local area can enjoy the same regeneration experiences by St Pancras and Kings Cross.
The suggestion of a Euston redevelopment comes just days after George Osborne made a similar comment.
McLoughlin also accepted this part of the report, saying: "I also agree with the report that more can be made of Euston station. It is a significant opportunity to maximise the economic potential of the line and regenerate a site that has been neglected."
A Department for Transport spokesman said: "HS2 is a vital part of our long-term economic plan. Not only will it link our northern cities and provide the extra space we need on our rail network, but it will provide and safeguard tens of thousands of jobs, giving people economic security for the future.
"Sir David Higgins' report supports this view and confirms that HS2 is the right project at the right price. But he has also set us a challenge – HS2 can be better and delivered quicker."