Rail investment should be focused on improving regional connections in the North and Midlands rather than completing the eastern section of HS2, the government's advisers have said.
The National Infrastructure Commission said better links between cities in the regions should be the priority as part of the wider strategy to "level up" the UK.
It found that this was likely to deliver economic benefits more quickly than the plan to extend the high-speed London-Birmingham link on to Leeds.
The assessment said it would be "potentially cheaper and faster" to deliver improvements to regional journeys through a combination of new lines and upgrades rather than phase 2b of HS2.
Sir John Armitt, chair of the commission, said money needed to be "carefully spent where it can make the most difference".
"The number and scale of rail schemes currently being proposed for the North and Midlands mean that some form of prioritisation will be necessary," he added.
"We think there are ways of bringing forward benefits for communities and businesses while keeping options open for additional investments if the circumstances are right."
Regional projects include Northern Powerhouse Rail between Liverpool and Hull and the Midlands Engine.
Focusing on these would boost the quality of often inferior east-west rail links in these areas and help cities such as Nottingham, Coventry, Derby, Manchester and Liverpool as well as smaller places including Crewe, Doncaster, Huddersfield and Warrington, the report said.
It would mean improvements for the journeys most people are most likely to take, into cities from the surrounding area, rather than into London, it added.
The commission was asked by the prime minister earlier this year to assess proposed rail schemes - though its remit did not cover phase 1 of HS2 from London to Birmingham or phase 2a on to Crewe.
Its report did not rule out "the further development of options to complete the HS2 Phase 2 eastern leg" but its findings were greeted with alarm by supporters of that project.
Maria Machancoses, director of regional transport lobby group Midlands Connect, described the report as "very concerning".
She said: "Sacrificing parts of the high-speed network now would short change millions of people across the Midlands and undermine our efforts to deliver a transport network fit for the 21st century."
Shadow transport secretary Jim McMahon said: "If the government is serious about improving British infrastructure, supporting jobs and improving connectivity in the North, it cannot now row back from building HS2 in its entirety."
The Department for Transport said it would take time to consider the recommendations and publish its integrated rail plan early next year.
HS2, Britain's biggest infrastructure project, was first mooted more than a decade ago and the go-ahead was given earlier this year for construction to begin.
It has been beset by delays and rising costs with some estimates putting the total bill at more than £100bn.
