Britain's train operators are preparing to launch a new railcard for those aged 26 to 59, promising a third off most train fares for pairs of passengers prepared to travel together.

Until now, the discount national railcards have required single or family users to be under 26, aged 60 plus, in the military, or travelling with children. However, now other rail users will be able to buy the new "Two Together" card which gives discounts for people aged 26-59 travelling together.

The Association of Train Operating Companies, which manages railcards and National Rail Enquiries, says the new railcard will give one-third off the cost of most rail tickets – but only if the two people named on the card travel together. The card will cost £30 a year and goes on sale at 9am on Monday 3 March.

People who buy the card will get one-third off many Standard and First Class Anytime, Off-Peak, Super Off-Peak and Advance fares, across the national rail network. The card also includes airport express services, and ferry-inclusive journeys such as trips to or from the Isle of Wight.

But the new Two Together discounted tickets are not available to be used between 4.30am and 9.30am on Mondays to Fridays. There are no restrictions on weekend trips.

Users must both be aged over 16. Forms will be available at a staffed stations, or online at twotogether-railcard.co.uk – for which you will need a digital passport photo of each person.

The discount applies only when both of you travel together. Any variation – such as only one of you making the return journey – renders the discounted tickets invalid. Depending on the policy of the train operator, you could be liable to pay the full Anytime fare or a penalty fare.

There is nothing to stop regular business users who travel with colleagues from using the card if their journey is after 9.30am. Equally, some passengers will want to buy more than one card so they can pair up with different people. Off-peak commuters need to find others who share the same trains, and join forces.

Those making long-distance journeys could save the £30 card's cost in one journey. A standard London-Birmingham off-peak round trip costs £50.50 per person on Virgin Trains, or £101 for two. The Two Together fare, plus the cost of a brand-new railcard, totals £96.70.