They are the first step in major reforms of the railways announced last month in the Williams-Shapps Plan for Rail.
Two-days-a-week commuters using flexible season tickets could save more than £260 travelling from Woking to London, £230 from Liverpool to Manchester, and £170 from Stafford to Birmingham, according to Department for Transport (DfT) analysis.
A passenger travelling to work three days per week from Chelmsford to Stratford, east London, could save in excess of £350.
The savings are compared with the cost of daily tickets.
The paperless flexible tickets, which can be used from June 28, will allow travel on any eight days in a 28-day period.
Passengers can use an updated season ticket calculator at www.nationalrail.co.uk to find out which ticket they should purchase based on their route and working pattern.
To encourage more people to travel to rail, train companies will allow passengers who buy an Advance ticket for a specific train to rebook or receive rail vouchers without an admin fee until the end of the year if their plans change.
Transport Secretary Grant Shapps said: “Our railways work best when they are reliable, rapid and affordable.
“As we kickstart the biggest reforms to our railways in a generation, flexible season tickets are the first step. They give us greater freedom and choice about how we travel, simpler ticketing and a fairer fare.
“With a season ticket calculator to see which option works best for you, and a book with confidence guarantee to make journeys stress-free, the future of fares is flexible.”
The introduction of flexible tickets comes amid changing travel patterns due to the coronavirus pandemic.
An increase in home working has led to a huge decline in the number of people travelling by rail, particularly those commuting rail five days a week.
Robert Nisbet, director of nations and regions at the Rail Delivery Group – which represents train operators, said: “We’ve worked with Government to introduce the new Flexi Season ticket, which goes on sale today, to give commuters the freedom and flexibility to divide their time between home and the office.
“The rail industry is helping people travel and book with confidence by providing better journey information, boosting cleaning and helping them change a booked journey fee free should their circumstances change.”
Anthony Smith, chief executive of passenger watchdog Transport Focus, said: “Some passengers will welcome today’s new flexible tickets and discounts. This will be useful in helping people choose rail again.
“Our research with passengers showed us there was strong demand for a new ticket that suited people who expected to commute less frequently in future.
“This is a positive step towards much-needed longer-term reform of how rail tickets are sold.”
Tickets offering discounts for part-time commuters were already available in Scotland and Wales.
The Williams-Shapps Plan for Rail will lead to the creation of a new public sector body named Great British Railways (GBR), which will own and manage rail infrastructure, issue contracts to private firms to run trains, set most fares and timetables, and sell tickets.
Rail franchises were effectively ended when the Government took over the financial liabilities of operators in March 2020 to keep services running amid the collapse in demand caused by the coronavirus pandemic, at a cost of £12 billion.
The emergency agreements will be replaced by passenger service contracts, with GBR contracting private firms to operate trains.