The Labour Party has warned scrapping rail electrification projects will lengthen journey times, increase carbon emissions and raise the cost of running the network.
Transport Secretary Chris Grayling announced last month that plans to electrify lines in Wales, the Midlands and the North have been cancelled or downgraded.
Labour claimed this will increase the duration of journeys such as between Manchester and Liverpool by nearly half an hour and between Leeds and Newcastle by over 20 minutes.
It also puts the estimated 19-minute journey time saving from new trains between Swansea and London at risk, according to the analysis.
Electrification can cut CO2 emissions by 20-30% compared with diesel trains and slash maintenance costs by a third, Labour said.
The party also accused the Government of undermining the Crossrail for the North project - boosting east-west rail services in northern England - as the route will not be fully electrified.