Road improvements may be delayed to enable ministers to funnel cash into Britain's ailing railway system, it emerged yesterday.

The transport secretary, Stephen Byers, is planning to help the rail network by using money earmarked for roads to invest instead in railway modernisation and renewal.

The plan would involve "borrowing" several billion pounds from the £60bn set aside for roads under the government's 10-year transport plan.

The transport department said the money would not be withdrawn from the roads budget permanently, but, in the short term, would skew spending towards rail.

The government had been planning to spend £60bn on roads, and the same on rail, with a remaining £60bn on improving local transport, as part of its £180bn public and private investment in transport announced last summer.

Ministers now realise more money must be spent on the rail network in the early stages of the plan than had been thought, leading to the plan for "borrowing" from the roads funds.

The reassessment illustrates how Mr Byers has been forced to address years of underinvestment by Railtrack and its predecessor British Rail. While transport officials deny roads will lose the cash earmarked under the 10-year plan, it could delay some projects.

A transport department spokesman said: "We will meet all our spending commitments within the 10-year plan, and there is no question of spending on any area, including roads, being disadvantaged. That will be clear when the local transport spending announcements are made later this month."

The transport minister, John Spellar, says in today's Financial Times: "We'll have to look at what the requirement is. We will then have to look at the balance between a variety of modes of transport.

"In Keynes's words, 'when circumstances change I change my mind'. We have to look at circumstances, but we also have to get the right balance."

The move comes after the chancellor, Gordon Brown, made it clear that health and education were government priorities in the new spending round, leaving the department of transport unlikely to receive any more funding.

Sacrificing road improvements for rail, even in the short term, will infuriate the car lobby. Edmund King, executive director of the RAC Foundation, said it would amount to "robbing Peter to pay Paul".