1/4 Network Rail has completed the latest stage of the £1.5bn Midland Main Line upgrade 2/4 It involves the biggest improvements to the line since it was built 3/4 Work will make way for electrification between London St Pancras International and Corby 4/4 Electric trains are more environmentally friendly than diesel trains Network Rail has completed the latest stage of the £1.5bn Midland Main Line upgrade, which involves the biggest improvements to the line since it was built. Work has been carried out to install new overhead line equipment between Bedford and Corby, as well as improvements to station platforms and major work to upgrade bridges on the route to make way for electrification between London St Pancras International and Corby.