A new scheme to compensate rail passengers for journeys delayed by just 15 minutes on some lines has created "unfairness" for those on the rest of the network, the head of the Commons' Transport Select Committee has warned.
Labour MP Louise Ellman, chairwoman of the committee, said the scheme should apply to journeys across Britain and urged the Department for Transport (DfT) to roll it out as soon as possible.
Passengers on Govia Thameslink Railway (GTR), the parent company of Southern, will be the first in the country to be eligible for payouts under Delay Repay 15 from December 11.
They will be able to claim compensation worth 25% of the cost of a single fare for delays of between 15 and 29 minutes.
But passengers travelling on trains run by other operators will not be eligible for compensation unless their journeys are at least half an hour late - even if they are travelling to or from the same station as GTR services.
The thresholds for compensation under the existing Delay Repay scheme are:
:: 50% of the single fare for delays of 30 to 59 minutes
:: 100% of the single fare for delays of 60 minutes or more
:: 100% of the return fare for delays of two hours or more
Ms Ellman, who has been the MP for Liverpool Riverside since 1997, said: "The department (DfT) has rightly prioritised the introduction of the Delay Repay 15 for GTR customers.
"However, this creates an unfairness for passengers on the rest of the network who can only claim when their trains are delayed by at least 30 minutes.
"We would like to hear when the DfT will roll out the scheme to the rest of the country - the sooner, the better."
The DfT said payouts after delays of 15 minutes will be included in all future rail franchises, starting with the new South Western, West Midlands and South Eastern franchises.
But many operators have agreements set to run for a number of years, such as Virgin Trains East Coast which has a contract to 2023.
The DfT said it is exploring opportunities to roll out Delay Repay 15 for all franchises during the current Parliament.
On Friday it was announced that some Southern passengers will be eligible for a separate one-off compensation package in recognition of the major disruption to services in recent months.
Some 84,000 season ticket holders will be able to claim a refund for the equivalent of a month's travel
Passengers with an annual ticket will be able to receive the payout against their 2016 ticket, which can be paid directly into their bank account.
Customers claiming against quarterly, monthly or weekly tickets must have bought travel for at least 12 weeks between April 24 and December 31 to be eligible.
The chaos on the Southern network has partly been caused by strikes over changes to the role of conductors and high levels of staff sickness.
It was also revealed on Friday that rail fares are being increased by an average of 2.3% from January 2.