Which may be summarised as "largely due to network rail, but not entirely"
Even for network rail, upgrading the power supply along an existing route should not be that hard. There is an existing 33KV distribution network along the railway, this feeds numerous transformer/rectifier stations.
Additional transformers and rectifiers are mature technology and available from several suppliers.
If the existing 33KV network is inadequate, then replacing the cables with larger ones is a simple task. HV cable is used in vast quantities by the electricity supply industry and is readily available.
Isn't it more like largely due to the
DfT» ?
The DfT specified the level of service they expected from the bids without checking with Network Rail if it was possible. The DfT won't give Network Rail funding for the work that would need to be done to make that level of service possible.