The UK Government's train carriage procurement programme requires an urgent reappraisal, according to Transport Secretary Philip Hammond.
Hammond's announcement comes in the wake of a report from the National Audit Office (NAO), the government-spending watchdog.
The new coalition government is forcing the Department for Transport to find £683m ($1bn) in savings as part of its efforts to slash the record deficit.
Under the last Labour government, which lost power after the May general election, 1,300 new carriages were to be delivered by 2012 to ease overcrowding on the national rail system.
Now all projects will be rigorously re-assessed to ensure value for money, Hammond said.
By March 2010, 526 of the new rolling stock had been delivered with a further 100 planned over the next two years.
Passenger traffic has doubled in the last decade.