LNER’s brand-new Azuma trains are to make their Scottish debut on 1 August, operating one service a day in each direction between Edinburgh and London.
The UK Government-run company was unable to say when more will be in service, including to Aberdeen and Inverness, but this is expected by the end of the year.
The first of the 65-strong fleet started running three weeks ago between London and Leeds, with a second added to the route last week.
LNER said they would only operate two Edinburgh services a day because of lack of Azumas delivered so far by manufacturers Hitachi.
They are five months late due to problems including their compatibility with signalling equipment.
LNER said the “electro-magnetic current interference” issue was due to be resolved by the end of this month.
The faster-accelerating trains will cut some Edinburgh-London journeys to four hours from the end of 2021, a saving of up to 40 minutes.
The first Scottish service will be the 0540 Edinburgh-King’s Cross “Flying Scotsman” on weekdays, the only one to already take just four hours.
An Azuma will also operate the weekday 1730 King’s Cross-Edinburgh service.
On Saturdays, the 0655 from Edinburgh and 1230 from London will feature the new trains. They will also operate the 0900 from Edinburgh and 1430 from London on Sundays.
The trains can operate on both electric and diesel power, enabling them to run as far as Aberdeen and Inverness because the lines north of Edinburgh are not electrified.
LNER said it expected the Azumas would run under electric power to Edinburgh in August.
However, it is understood they may have to run on diesel for part of the way if an electrical power upgrade north of Doncaster is delayed.
An LNER spokeswoman said: “Azuma trains are being phased in as the existing fleet of trains are phased out of service. This programme is due to be complete by summer next year.
“We are currently planning on running in electric mode but it will be a bi-mode train should any diesel power be required.”
The trains will each add up to 100 extra seats per service, have 7cm more leg room in standard class and free wi-fi.
Scottish Secretary David Mundell said: “Improved train services make it easier for Scottish businesses to reach their customers and will attract more visitors to Scotland, helping to boost jobs and prosperity.”