ScotRail have been accused of introducing “new” trains – with 10million miles on the clock.
A fleet of refurbished InterCity 125 trains will come into service on routes from Glasgow and Edinburgh to Inverness and Aberdeen next year.
The 26 high-speed trains date back 40 years. They were introduced by British Rail in 1977.
Having travelled about 1000 miles a day, they have now each covered about 10million miles.
The InterCity 125s are being used by Great Western Railway in England, where replacement electric stock is being phased in.
They are being leased for 12 years by Dutch operators Abellio, who will spend £54million refurbishing them.
Manuel Cortes, leader of the Transport Salaried Staffs’ Association, said: “The InterCity 125 was a fine high-speed train when it came on track in the 1970s.
“But it is far from a high-speed train now. You wouldn’t expect the police to drive round in a Rover 2000 and call it high powered today.”
The InterCity 125 is still popular among rail enthusiasts. David Shirres, editor of Rail Engineer magazine, said the trains would provide a more comfortable journey for passengers.
He said: “During their lifetime, all major components have been replaced many times over and are subject to regular inspections and repairs. The bodywork is being stripped back to basics and any corroded bodywork will be repaired and made good for 10-15 years.
“They are good trains that arguably saved British Rail in the sense that when they were built they were ahead of their time in terms of design and performance.
“I do not see any problems whatsoever and I think they will provide a very good passenger environment. They will be far superior to the trains currently on these routes.”
ScotRail are also putting into service 70 electric trains on the main Edinburgh-Glasgow line and other key routes.
A ScotRail Alliance spokesman said: “We are spending £54million refurbishing our high-speed train fleet, transforming long-distance rail travel in Scotland by providing more seats and a much improved on-board environment.
“The trains will be fitted with wifi, new CCTV cameras, powered doors and passenger information systems.
“A galley catering and buffet area will showcase high quality Scottish food and drink. A first class coach and additional storage areas for luggage will also feature.”
A Transport Scotland spokesman said: “When the 121 high-speed train coaches are introduced into service, this will provide 40 per cent more seats on inter-city routes compared to today.
“It is always significant to note that the quality of the vehicle is important, not its age.
“Good, high quality refurbishment can deliver a passenger experience comparable with new rolling stock.”