Rail passengers will now be able to buy cheaper "advance" tickets on the day of departure, the Rail Delivery Group (RDG) said on Wednesday (5 July).
Up until now, passengers were allowed to purchase "advance" tickets, which were first introduced by CrossCounty in 2015 and enable customers to book the lowest fare on the day of travel, until midnight the day before departure.
However, under the new system, the option will be available until 10 minutes before their service is scheduled to depart.
"Not everyone can plan journeys in advance and now more people can buy cheaper tickets on the day, even on their way to the station," said RDG managing director of customer experience Jacqueline Starr.
"We want customers to get the best possible deal whenever they travel."
While advance fares are limited to a number of seats and tend to sell out fairly quickly, they also offer substantial savings. For example, a single fare for the 2.20pm service between London Euston and Manchester Piccadilly for Wednesday (5 July) would have costed £82.90 in purchased online today.
Booking a ticket for the same service on Tuesday (11 July) six days in advance would instead cost just £38.
The RDG said advance tickets to be bought on the day of travel will be available on CrossCounty, Grand Central, Greater Anglia, Northern, Transpennine Express, Virgin Trains East Coast, Virgin West Coast and Caledonian Sleeper.
However, they are not being offered on Arriva Trains Wales, South West Trains, Southern, Southeastern, ScotRail or First Great Western.
"We welcome this initiative which removes a further barrier to affordable rail travel and means people can make unplanned journeys without being unfairly penalised," said Lianna Etkind, public transport campaigner at Campaign for Better Transport.
"We would urge train companies not already signed up to this to follow suit so all passengers benefit from these new tickets. However, we hope this doesn't add another layer of complexity to a ticketing system already bloated and convoluted."