For fuel use, that must depend on the national electricity supply's carbon status. Otherwise the boundary you draw can include more or less extra stuff if you want, like building the trains or indeed feeding the staff! But why would new electric trains be very different from old ones? Faster ones use more juice, of course, which must be more relevant.
All they need to do is sign up to one of the "100% Green" tariffs, available from all good suppliers*.
(*And most bad ones)Network rail have (perhaps) one of those. Their traction electricity contract with EDF was announced in 2013 as matching their use with nuclear generation. However, in
a summary of their utilities contracts in 2017 they didn't mention that aspect. They did say this:
The Traction Electricity contract was signed with EDF Energy in January 2013 and runs for 10 years from 1st October 2014 to 30th September 2024. The scope includes all imported electricity through traction supply points (around 120) and the export of surplus regenerated electricity. It is a flexible contract and the only element fixed at the outset was the management fee. All other cost elements are passed through by EDF Energy once the actual rates are known.
Total Consumption in 2016-17 is around 3,400,000,000 kWh (3,400GWh) and will cost around ?300m.
...
Appendix A shows a breakdown of the various cost elements. The commodity or power station gate price now makes up less than half of the total cost. The price must be locked ahead of the month of delivery. Network Rail has passed responsibility for locking the price to the train operators (except for the NTfT portion). The commodity price can be locked up to the end of the contract.
