Seven rail firms have agreed to sell passengers cheaper Advance tickets up to just 10 minutes before their journey begins.
The measure to enable travellers to book the lowest fares on the day of travel was first introduced by CrossCountry in 2015.
The Rail Delivery Group (RDG), representing train operators, said it has now been implemented by Grand Central, Greater Anglia, Northern, TransPennine Express, Virgin Trains East Coast, Virgin Trains West Coast and Caledonian Sleeper.
Passengers travelling on some services run by these firms can now buy an Advance ticket as little as 10 minutes before their train departs, helping those who need to make short notice travel plans.
The tickets have previously been withdrawn from sale at midnight on the day before travel.
RDG managing director of customer experience Jacqueline Starr said: "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.
"We want customers to get the best possible deal whenever they travel."
Lianna Etkind of the Campaign for Better Transport said: "We welcome this initiative which removes a further barrier to affordable rail travel and means people can make unplanned journeys without being unfairly penalised.
"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."