Three travel classes will be available on a domestic UK railway line for the first time in more than 60 years.
Avanti West Coast, which has replaced Virgin Trains on the West Coast Main Line, will offer premium economy as well as standard and first-class seats.
The new middle-tier fares have not yet been revealed.
The operator has also vowed to improve the carriages used, with a £117m refurbishment of the Pendolinos and a replacement for the Super Voyagers.
Matthew Gregory, chief executive of FirstGroup, which owns the franchise with Italian firm Trenitalia, said the change in policy was “about seeing if we can offer a more flexible offering that suits more price points”.
Third-class rail travel was abolished in Britain in 1956 and renamed second class before later being branded standard class.
In Italy, Trenitalia has four classes on its high-speed Frecciarossa services, while cross-Channel rail operator Eurostar offers three classes of travel.
Rail expert Mark Smith, founder of Seat61.com, said: “When it comes to intercity travel, there does seem to be scope for having some extra classes, but it depends what they’re doing and how they’re doing it.”
The operator has also announced plans to double the frequency of services on its London-Liverpool route to two trains an hour.
“With the modelling that we’ve carried out, we believe Liverpool is a market that is underserved,” said FirstGroup managing director Steve Montgomery.
“If you’ve got a half-hour frequency, people are more inclined just to turn up and go. I think that’s really important for that market.”
The operator has also promised to improve catering on board its services and offer more reliable wi-fi.