The Government's plans for the HS2 high-speed rail project between Birmingham and London must not lead to less investment in the rest of the network, a transport campaign group has said.
Budgets could be cut on other rail schemes while the Government concentrates on HS2, the Campaign for Better Transport (CBT) said.
Its comments came ahead of a Government launch next week of consultation on HS2 which could cost around £33 billion if the section north of Birmingham goes ahead.
CBT director Richard Hebditch said: "High speed rail (HSR) could offer an opportunity to improve transport in the UK and provide greener choices for long-distance travel.
"But the danger is that the Government is so focused on just getting plans through in the face of local opposition that it ignores the need for it to be part of improving the whole network."
He went on: "We're very worried that ministers will need to cut budgets elsewhere to pay for HSR. That could mean even steeper fare rises and cuts in local rail services in order to pay for it.
"And the best way for rail to offer a greener alternative is to electrify much more of the network but plans for electrification could be put back as HSR eats up all the funding."
Also on Thursday, 69 top businessmen, including CBI director-general John Cridland and former British Airways chief executive Willie Walsh, gave their backing for HS2.
In a letter to the Financial Times, the top bosses, including chambers of commerce leaders, said HSR would boost the British economy, create new jobs and improve growth prospects.
Transport Secretary Philip Hammond said: "We cannot afford not to invest in our future. All other major economies are pressing ahead with ambitious HSR plans - Britain must not be left behind.
"However, we have been quite clear that investing in HSR isn't something we will do instead of improving commuter services, but in addition."