TransPennine Express launched services between Newcastle and Edinburgh on the east coast main line last Sunday, but its Nova 1 trains are barred from using the overhead wires over part of the line.
The 18 trains a day – which will increase to 32 in January – have to use diesel engines instead between Chathill in Northumberland and Longniddry in East Lothian.
Several of LNER’s new Azuma trains, which are also dual power, are affected too.
Further Azuma-hauled services may need to switch to diesel in 2021 so there is enough power to enable operator First to run planned rival Edinburgh-London electric-only trains.
The problem has arisen because the necessary upgrades by Network Rail have not been taken into account when train operators have announced new train fleets and extra services.
The UK government-owned body said substations feeding electricity to the line may not be boosted until 2022.
Friends of the Earth Scotland director Richard Dixon said: “It is farcical that electric trains are having to use diesel when electricity is flowing through cables just a few feet above them, needlessly adding to climate change.
“It has been obvious for years that, in order to reduce both climate emissions and local air pollution issues, electric trains are the way forward.
“The failure to invest to make sure that enough power is available is inexcusable.”
Scottish Association for Public Transport chair John McCormick said: “Electrified railways have a crucial role in achieving the government’s zero emission targets for transport.
“The rail’s market share of Anglo-Scottish travel is increasing but the full environmental benefits will be missed if diesel has to be used to power trains under overhead wires – a ludicrous situation.”
A TransPennine Express spokesman said: “We are running our Nova 1 trains between Newcastle and Edinburgh on diesel power for pre-defined short sections. This is in agreement with Network Rail, who have factored in the available power supply at these peak demand times on that section of track.”
A Network Rail spokesperson said: “We are delivering a £1.2bn upgrade of the east coast main line.
“As part of that investment we will be improving the power supply on the line between Edinburgh and Berwick to allow more electric trains to run.”